XTO ENERGY INC. $250,000,000 5.000% Senior Notes due 2010 $500,000,000 5.750% Senior Notes due 2013 $1,000,000,000 6.500% Senior Notes due 2018 $500,000,000 6.750% Senior Notes due 2037 UNDERWRITING AGREEMENT

EXHIBIT 1.6

Execution Copy

$2,250,000,000

XTO ENERGY INC.

$250,000,000 5.000% Senior Notes due 2010

$500,000,000 5.750% Senior Notes due 2013

$1,000,000,000 6.500% Senior Notes due 2018

$500,000,000 6.750% Senior Notes due 2037

UNDERWRITING AGREEMENT

August 4, 2008

XXXXXX BROTHERS INC.

BANC OF AMERICA SECURITIES LLC

as Representatives of the Underwriters

set forth on Schedule I hereto

c/x Xxxxxx Brothers Inc.

000 Xxxxxxx Xxxxxx

Xxx Xxxx, Xxx Xxxx 00000

Ladies and Gentlemen:

XTO Energy Inc., a Delaware corporation (the “Company”), proposes to issue and sell $250,000,000 aggregate principal amount of its 5.000% Senior Notes due 2010 (the “2010 Notes”), $500,000,000 aggregate principal amount of its 5.750% Senior Notes due 2013 (the “2013 Notes”), $1,000,000,000 aggregate principal amount of its 6.500% Senior Notes due 2018 (the “2018 Notes”) and $500,000,000 aggregate principal amount of its 6.750% Senior Notes due 2037 (the “2037 Notes”) (collectively, the 2010 Notes, 2013 Notes, 2018 Notes and 2037 Notes are herein referred to as the “Notes”) to you (the “Underwriters”). The Notes will be issued pursuant to an Indenture dated as of July 19, 2007, as amended and supplemented to date, and as further amended and supplemented by a Third Supplemental Indenture to be dated on or before the Delivery Date (as defined in Section 4), (collectively, the “Indenture”) between the Company and The Bank of New York Mellon Trust Company, N.A., as Trustee (the “Trustee”). This agreement (this “Agreement”) is to confirm the agreement concerning the purchase of the Notes from the Company by the Underwriters.

Section 1. Representations, Warranties and Agreements of the Company. The Company represents, warrants and agrees that:

(a) A registration statement on Form S-3 relating to the Notes (File No. 333-135136) (i) has been prepared by the Company in conformity with the requirements of the

Securities Act of 1933, as amended (the “Securities Act”), and the rules and regulations (the “Rules and Regulations”) of the Securities and Exchange Commission (the “Commission”) thereunder; (ii) has been filed with the Commission under the Securities Act; and (iii) upon its filing with the Commission automatically became and is effective under the Securities Act. Copies of such registration statement and any amendment thereto and any supplement to the prospectus included therein have been made available by the Company to you as the representatives (the “Representatives”) of the Underwriters; and no other document relating to the Notes with respect to such registration statement or any such document incorporated by reference therein has heretofore been filed or transmitted for filing with the Commission. As used in this Agreement:

(i) “Applicable Time” means 6:00 p.m. (New York City time) on the date of this Agreement;

(ii) “Base Prospectus” means the base prospectus filed as part of the Registration Statement, in the form in which it has most recently been amended on or prior to the date hereof, relating to the Notes;

(iii) “Effective Date” means any date as of which any part of such registration statement relating to the Notes became, or is deemed to have become, effective under the Securities Act in accordance with the Rules and Regulations;

(iv) “Final Term Sheet” means the term sheet prepared pursuant to Section 5(a) of the Agreement and substantially in the form attached in Schedule III hereto;

(v) “Issuer Free Writing Prospectus” means each “free writing prospectus” (as defined in Rule 405 of the Rules and Regulations) prepared by or on behalf of the Company or used or referred to by the Company in connection with the offering of the Notes, including the Final Term Sheet;

(vi) “Preliminary Prospectus” means any preliminary prospectus relating to the Notes included in such registration statement, including the Base Prospectus, or filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations, including any preliminary prospectus supplement thereto relating to the Notes, and provided to the Representatives for use by the Underwriters;

(vii) “Pricing Disclosure Package” means, as of the Applicable Time, the most recent Preliminary Prospectus, together with each Issuer Free Writing Prospectus filed or used by the Company on or before the Applicable Time and identified on Schedule II, other than a road show that is an Issuer Free Writing Prospectus under Rule 433 of the Rules and Regulations;

(viii) “Prospectus” means the final prospectus relating to the Notes, including the Base Prospectus and any final prospectus supplement thereto

relating to the Notes, as filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations and provided to the Representatives for use by the Underwriters; and

(ix) “Registration Statement” means, collectively, the various parts of such registration statement, each as amended as of the Effective Date for such part, including any Preliminary Prospectus or the Prospectus and all exhibits to such registration statement.

Any reference to any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include any documents incorporated by reference therein pursuant to Form S-3 under the Securities Act as of the date of such Preliminary Prospectus or the Prospectus, as the case may be. Any reference to the “most recent Preliminary Prospectus” shall be deemed to refer to the latest Preliminary Prospectus included in the Registration Statement or filed pursuant to Rule 424(b) prior to or on the date hereof (including, for purposes hereof, any documents incorporated by reference therein prior to or on the date hereof). Any reference to any amendment or supplement to any Preliminary Prospectus or the Prospectus shall be deemed to refer to and include any document filed under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), after the date of such Preliminary Prospectus or the Prospectus, as the case may be, and incorporated by reference in such Preliminary Prospectus or the Prospectus, as the case may be; and any reference to any amendment to the Registration Statement shall be deemed to include any annual report of the Company on Form 10-K filed with the Commission pursuant to Section 13(a) or 15(d) of the Exchange Act after the Effective Date that is incorporated by reference in the Registration Statement. The Commission has not issued any order preventing or suspending the use of any Preliminary Prospectus, the Prospectus, any Issuer Free Writing Prospectus or of any document incorporated by reference in the most recent Preliminary Prospectus or suspending the effectiveness of the Registration Statement, and no proceeding or examination for such purpose has been instituted or threatened by the Commission. The Commission has not notified the Company of any objection to the use of the form of the Registration Statement.

(b) The Company has been since the time of initial filing of the Registration Statement and continues to be a “well-known seasoned issuer” (as defined in Rule 405) eligible to use Form S-3 for the offering of the Notes, including not having been an “ineligible issuer” (as defined in Rule 405) at any such time or date. The Registration Statement is an “automatic shelf registration statement” (as defined in Rule 405) and was filed not earlier than the date that is three years prior to the Delivery Date.

(c) The Registration Statement conformed and will conform in all material respects on the Effective Date and on the Delivery Date, and any amendment to the Registration Statement filed after the date hereof will conform in all material respects when filed, to the requirements of the Securities Act and the Rules and Regulations. The most recent Preliminary Prospectus conforms on the date hereof, and the Prospectus and any amendment or supplement thereto will conform, in all material respects when filed with the Commission pursuant to Rule 424(b) and on the Delivery Date to the requirements of the Securities Act and the Rules and Regulations.

(d) The Pricing Disclosure Package did not, as of the Applicable Time, contain an untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, that no representation or warranty is made as to information contained in or omitted from the Registration Statement in reliance upon and in conformity with written information furnished to the Company through the Representatives by or on behalf of any Underwriter specifically for inclusion therein, which information is specified in Section 9(e).

(e) Each Issuer Free Writing Prospectus (including, without limitation, any road show that is a free writing prospectus under Rule 433), when considered together with the Pricing Disclosure Package as of the Applicable Time, did not contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading. Each Issuer Free Writing Prospectus (including, without limitation, any road show that is a free writing prospectus under Rule 433) does not include any information that conflicts with the information contained in the Registration Statement, including any document incorporated by reference therein that has not been superseded or modified, or the Pricing Disclosure Package.

(f) Each Issuer Free Writing Prospectus (including, without limitation, any road show that is a free writing prospectus under Rule 433) conformed or will conform in all material respects to the requirements of the Securities Act and the Rules and Regulations on the date of first use, and the Company has complied with any filing requirements applicable to such Issuer Free Writing Prospectus pursuant to the Rules and Regulations. The Company has not made any offer relating to the Notes that would constitute an Issuer Free Writing Prospectus without the prior written consent of the Representatives. The Company has retained, and will retain, in accordance with the Rules and Regulations all Issuer Free Writing Prospectuses that were not required to be filed pursuant to the Rules and Regulations.

(g) The Registration Statement did not, as of the Effective Date, and the Prospectus will not, as of its date and on the Delivery Date, contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading; provided, that no representation or warranty is made as to information contained in or omitted from the Registration Statement or the Prospectus in reliance upon and in conformity with written information furnished to the Company through the Representatives by or on behalf of any Underwriter specifically for inclusion therein, which information is specified in Section 9(e).

(h) The documents incorporated by reference in any Preliminary Prospectus or the Prospectus conformed, and any further documents so incorporated will conform,

when filed with the Commission, in all material respects to the requirements of the Exchange Act or the Securities Act, as applicable, and the rules and regulations of the Commission thereunder. None of such documents, when filed with the Commission, contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading.

(i) Neither the Company nor any of its subsidiaries has sustained, since the date of the latest audited financial statements included in the Preliminary Prospectus, any material loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor dispute or court or governmental action, order or decree, otherwise than as set forth or contemplated in the Preliminary Prospectus or Prospectus; and, since the respective dates as of which information is given in the Registration Statement and the Preliminary Prospectus, there has not been any change in the long-term debt of the Company or any of its subsidiaries, other than changes to indebtedness outstanding under the Company’s Term Loan Agreement dated November 10, 2004, as amended, between the Company and Bank of America, as Administrative Agent, and the other lenders, the Company’s Term Loan Agreement dated February 5, 2008, between the Company and The Royal Bank of Scotland Finance (Ireland), the Company’s Amended and Restated 5-Year Revolving Credit Agreement dated April 1, 2005 between the Company and certain commercial banks named therein, as amended to date, and the Company’s commercial paper program, or any material adverse change, or any development involving a prospective material adverse change, in or affecting the general affairs, management, financial position, stockholders’ equity or results of operations of the Company and its subsidiaries, otherwise than as set forth or contemplated in the Preliminary Prospectus.

(j) (1) The Company has good and defensible title to all real property, free and clear of all liens, encumbrances and defects, except (A) royalties, overriding royalties and other burdens under oil and gas leases, (B) easements, restrictions, rights-of-way and other matters that commonly affect property, (C) liens securing taxes and other governmental charges, or claims of materialmen, mechanics and similar persons, not yet due and payable, (D) liens and encumbrances under operating agreements, farmout agreements, unitization, pooling and commutation agreements, declarations and orders, and gas sales contracts, securing payment of amounts not yet due and payable and of a scope and nature customary in the oil and gas industry and (E) liens, encumbrances and defects that do not in the aggregate materially affect the value of the real property or materially interfere with the use made or proposed to be made of such real property by the Company; and (2) the working interests in oil, gas and mineral leases or mineral interests which constitute a portion of the real property held by the Company reflect in all material respects the right of the Company to explore or receive production from such real property, and the care taken by the Company and its subsidiaries with respect to acquiring or otherwise procuring such leases or mineral interests was generally consistent with standard industry practices for acquiring or procuring leases and interests therein to explore for hydrocarbons.

(k) The Company has been duly incorporated and is validly existing as a corporation in good standing under the laws of Delaware, is duly qualified to do business and is in good standing as a foreign corporation in each jurisdiction in which its ownership or lease of property or the conduct of its business requires such qualification, and has all power and authority necessary to own or hold its properties and to conduct the businesses in which it is engaged; and none of the subsidiaries of the Company is a significant subsidiary, as such term is defined in Rule 405 of the Rules and Regulations.

(l) The Company has an authorized capitalization as set forth in the most recent Preliminary Prospectus and the Prospectus. All of the issued shares of capital stock of the Company have been duly and validly authorized and issued, were issued in compliance with federal and state securities laws, are fully paid and non-assessable and conform, or will conform, to the description thereof contained in the Registration Statement, the most recent Preliminary Prospectus and the Prospectus. All of the Company’s options, warrants and other rights to purchase or exchange any securities for shares of the Company’s capital stock have been duly and validly authorized and issued, were issued in compliance with federal and state securities laws, and conform, or will conform, to the description thereof contained in the Registration Statement, the most recent Preliminary Prospectus and the Prospectus. All of the issued shares of capital stock of each subsidiary of the Company have been duly authorized and validly issued, are fully paid and non-assessable and are owned directly or indirectly by the Company, free and clear of all liens, encumbrances, equities or claims, except for such liens, encumbrances, equities or claims as could not, in the aggregate, reasonably be expected to have a material adverse effect.

(m) Neither (i) the execution or delivery hereof by the Company, nor (ii) the consummation of the transactions contemplated hereby, nor (iii) the execution and delivery of the Indenture and the Notes by the Company, nor (iv) the application of the proceeds from the sale of the Notes as described under “Use of Proceeds” in the most recent Preliminary Prospectus, nor (v) compliance by the Company with all of the provisions of this Agreement, the Indenture and the Notes, will (A) conflict with or result in a breach or violation of, or constitute a default under, the certificate of incorporation, by-laws, partnership agreement or other governing documents of the Company or any of its subsidiaries, or any material agreement, indenture or other instrument to which the Company or any of its subsidiaries is a party or by which any of them is bound, or to which any of their properties is subject or (B) violate any law, rule, administrative regulation or decree of any court, or any governmental agency or body having jurisdiction over the Company, its subsidiaries or any of their respective properties or assets, or result in the creation or imposition of any lien, charge, claim or encumbrance upon any property or asset of the Company or any of its subsidiaries, which in any such event described in this subclause (B) would have a material adverse effect on the Company. Except for (i) the registration of the Notes under the Securities Act, (ii) such consents, approvals, authorizations, registrations or qualifications as may be required under the Exchange Act and applicable state securities laws in connection with the purchase and sale of the Notes by the Underwriters and such permits, consents, approvals and similar authorizations

required under the securities or “Blue Sky” laws of certain jurisdictions, and (iii) such permits, consents, approvals and authorizations which have been obtained, no permit, consent, approval, authorization or order of, or filing or registration with, any court, governmental agency or body or financial institution is required in connection with the consummation of the transactions contemplated by this Agreement.

(n) Neither the Company nor any of its subsidiaries is in violation of its certificate of incorporation or bylaws or in default in the performance or observance of any material obligation, agreement, covenant or condition contained in any indenture, mortgage, deed of trust, loan agreement, lease or any other agreement or instrument to which it is a party or by which it or any of its properties is bound.

(o) The Company has all requisite corporate power and authority to execute, deliver and perform its obligations under this Agreement. This Agreement has been duly authorized, executed and delivered by the Company.

(p) The Notes will rank pari passu with all existing and future unsecured and unsubordinated indebtedness of the Company.

(q) The Indenture has been duly and validly authorized, and, on or prior to the Delivery Date, will be executed and delivered by the Company and will be a valid and binding agreement of the Company, enforceable against the Company in accordance with its terms, except as the enforceability thereof may be limited by bankruptcy, insolvency, reorganization or similar laws relating to or affecting creditors’ rights generally and by general equitable principles (regardless of whether such enforceability is considered in a proceeding in equity or at law). The Indenture (i) is duly qualified under the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”), (ii) complies as to form with the requirements of the Trust Indenture Act and (iii) conforms, or will conform, to the description thereof in the Registration Statement, the Preliminary Prospectus and the Prospectus.

(r) The Notes have been duly and validly authorized by the Company for issuance and sale to the Underwriters pursuant to this Agreement and, when executed by the Company and authenticated by the Trustee in accordance with the Indenture and delivered to the Underwriters against payment therefor in accordance with the terms hereof, will have been validly issued and delivered, free of any preemptive or similar rights to subscribe to or purchase the same arising by operation of law or under the charter or by-laws of the Company or otherwise, and will constitute valid and binding obligations of the Company entitled to the benefits of the Indenture and enforceable in accordance with their terms, except as enforcement thereof may be limited by bankruptcy, insolvency, reorganization or other similar laws relating to or affecting the enforcement of creditors’ rights generally and by general equitable principles, and the Notes conform, or will conform, to the description thereof in the Registration Statement, the Preliminary Prospectus and the Prospectus. The Company has all requisite corporate power and authority to issue, sell and deliver the Notes in accordance with and upon the terms and

conditions set forth in this Agreement and in the Registration Statement, the Preliminary Prospectus and Prospectus. All corporate action required to be taken by the Company for the authorization, issuance, sale and delivery of the Notes to be sold by the Company hereunder has been validly and sufficiently taken.

(s) The financial statements (including the related notes and supporting schedules) filed as part of the Registration Statement or included or incorporated by reference in the most recent Preliminary Prospectus and the Prospectus comply as to form in all material respects with the requirements of Regulation S-X under the Securities Act and present fairly the financial condition, results of operations and the cash flows of the entities purported to be shown thereby, at the dates and for the periods indicated, and have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the periods involved.

(t) The Company has not sold or issued any securities that would be integrated with the offering of the Notes contemplated by this Agreement pursuant to the Securities Act, the Rules and Regulations or the interpretations thereof by the Commission.

(u) KPMG LLP (“KPMG”), who have certified certain financial statements of the Company, whose reports appear in the Preliminary Prospectus and the Prospectus or are incorporated by reference therein and who have delivered the initial letter referred to in Section 8(f) hereof, are independent registered public accountants within the meaning of Rule 101 of the Code of Professional Conduct of the American Institute of Certified Public Accountants and its interpretations and rulings thereunder.

(v) The Company and each of its subsidiaries carry, or are covered by, insurance in such amounts and covering such risks as is adequate for the conduct of their respective businesses and the value of their respective properties as is customary for companies engaged in similar businesses in similar industries.

(w) The Company and each of its subsidiaries own or possess adequate rights to use all material patents, patent applications, trademarks, service marks, trade names, trademark registrations, service xxxx registrations, copyrights and licenses necessary for the conduct of their respective businesses and have no reason to believe that the conduct of their respective businesses will conflict with, and have not received any notice of any claim of conflict with, any such rights of others.

(x) Except as described in the most recent Preliminary Prospectus and the Prospectus, there are no legal or governmental proceedings pending to which the Company or any of its subsidiaries is a party or of which any property or assets of the Company or any of its subsidiaries is the subject which, if determined adversely to the Company or any of its subsidiaries, would have a material adverse effect on the consolidated financial position, stockholders’ equity, results of operations, business or prospects of the Company and its subsidiaries; and to the best of the Company’s knowledge, no such proceedings are threatened or contemplated by governmental authorities or threatened by others.

(y) No labor disturbance by the employees of the Company or its subsidiaries exists or, to the knowledge of the Company, is imminent, which could be reasonably expected to have a material adverse effect on the general affairs, management, consolidated financial position, stockholders’ equity, results of operations, business or prospects of the Company and its subsidiaries.

(z) Since the date as of which information is given in the most recent Preliminary Prospectus through the date hereof, and except as may otherwise be disclosed in the most recent Preliminary Prospectus and the Prospectus, the Company has not (i) issued or granted any securities other than pursuant to any of its employee benefit plans, (ii) incurred any liability or obligation, direct or contingent, other than liabilities and obligations which were incurred in the ordinary course of business or (iii) entered into any transaction not in the ordinary course of business.

(aa) The Company (i) makes and keeps accurate books and records and (ii) maintains internal accounting controls which provide reasonable assurance that (A) transactions are executed in accordance with management’s authorization, (B) transactions are recorded as necessary to permit preparation of its financial statements and to maintain accountability for its assets, (C) access to its assets is permitted only in accordance with management’s authorization and (D) the reported accountability for its assets is compared with existing assets at reasonable intervals.

(bb) Neither the Company nor any of its subsidiaries, nor any director, officer, agent, employee or other person acting on behalf of the Company or any of its subsidiaries, has (i) used any corporate funds for any unlawful contribution, gift, entertainment or other unlawful expense relating to political activity, (ii) made any direct or indirect unlawful payment to any foreign or domestic government official or employee from corporate funds, (iii) violated or is in violation of any provision of the Foreign Corrupt Practices Act of 1977, or (iv) made any bribe, rebate, payoff, influence payment, kickback or other unlawful payment. Neither the Company nor any of its subsidiaries conducts business or has any operations in any foreign jurisdiction.

(cc) There has been no storage, disposal, generation, manufacture, refinement, transportation, handling or treatment of toxic wastes, medical wastes, hazardous wastes or hazardous substances by the Company or any of its subsidiaries (or, to the knowledge of the Company, any of their predecessors in interest) at, upon or from any of the property now or previously owned or leased by the Company or its subsidiaries in violation of any laws, regulations, ordinances, rules, orders, judgments, decrees, permits or other legal requirements of any governmental authority, including without limitation any international, national, state, provincial, regional, or local authority, relating to the protection of human health or safety, the environment, or natural resources, or to hazardous or toxic substances or wastes, pollutants or contaminants (“Environmental

Laws”) or which would require remedial action under any applicable Environmental Laws, except for any violation or remedial action which would not be reasonably likely to have, singularly or in the aggregate with all such violations and remedial actions, a material adverse effect on the general affairs, management, consolidated financial position, stockholders’ equity or results of operations of the Company and its subsidiaries; there has been no material spill, discharge, leak, emission, injection, escape, dumping or release of any kind onto such property or into the environment surrounding such property of any toxic wastes, medical wastes, solid wastes, hazardous wastes or hazardous substances due to or caused by the Company or any of its subsidiaries or with respect to which the Company or any of its subsidiaries have knowledge, except for any such spill, discharge, leak, emission, injection, escape, dumping or release which would not be reasonably likely to have, singularly or in the aggregate with all such spills, discharges, leaks, emissions, injections, escapes, dumpings and releases, a material adverse effect on the general affairs, management, consolidated financial position, stockholders’ equity or results of operations of the Company and its subsidiaries; and the terms “hazardous wastes,” “toxic wastes,” “hazardous substances” and “medical wastes” shall have the meanings specified in any applicable Environmental Laws; none of the Company or any of its subsidiaries has received notice of any actual or alleged violation of such Environmental Laws, or of any potential liability for or other obligation concerning the presence, disposal or release of hazardous or toxic substances or wastes, pollutants or contaminants, which violations or liabilities could reasonably be expected to have a material effect on the capital expenditures, earnings or competitive position of the Company and its subsidiaries. Except as described in the most recent Preliminary Prospectus, (A) there are no proceedings that are pending, or known to be contemplated, against the Company or any of its subsidiaries under Environmental Laws in which a governmental authority is also a party, other than the Notice of Violation issued February 1, 2008 from the Division of Air Quality of the Department of Environmental Conservation of the State of Alaska and other than such proceedings regarding which it is reasonably believed no monetary sanctions of $100,000 or more will be imposed, (B) the Company and its subsidiaries are not aware of any issues regarding compliance with Environmental Laws, or liabilities or other obligations under Environmental Laws or concerning hazardous or toxic substances or wastes, pollutants or contaminants, which could reasonably be expected to have a material effect on the capital expenditures, earnings or competitive position of the Company and its subsidiaries, and (C) none of the Company and its subsidiaries anticipates material capital expenditures relating to Environmental Laws.

(dd) The Company is not, and after giving effect to the offer and sale of the Notes and the application of the proceeds therefrom as described under “Use of Proceeds” in the most recent Preliminary Prospectus and the Prospectus will not be, an investment company as defined in the Investment Company Act of 1940, as amended (the “Investment Company Act”).

(ee) The information supplied by the Company to its independent petroleum engineering consultants for purposes of preparing the reserve reports used to calculate

estimates of reserves of the Company included in the Registration Statement, Preliminary Prospectus and Prospectus, including, without limitation, production, costs of operation and development, current prices for production, agreements relating to current and future operations and sales of production, was true and correct in all material respects on the date supplied and was prepared in accordance with customary industry practices; Xxxxxx and Xxxxx, Ltd., independent consulting petroleum engineers, who prepared estimates of the extent and value of proved oil and natural gas reserves, are independent with respect to the Company.

(ff) The Company has not taken and will not take, directly or indirectly, any action which is designed to or which has constituted or which would reasonably be expected to cause or result in stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Notes.

(gg) There are no contracts, agreements or understandings between the Company and any person granting such person the right (other than rights which have been waived or satisfied) to require the Company to file a registration statement under the Securities Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to the Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Securities Act (other than (i) the Registration Rights Agreement dated May 11, 1993 by and between the Company and certain stockholders (the “1993 Registration Rights Agreement”) under which all registrable securities are eligible for trading pursuant to Rule 144 under the Securities Act, (ii) the Registration Rights Agreement dated July 15, 2008 by and between the Company and Headington Oil Company LLC and other sellers under which all registrable securities are currently registered pursuant to the Registration Statement and the terms of which require the Company to file a registration statement in the event the registrable securities may not be sold under the Registration Statement prior to the expiration of the one-year registration period and (iii) the registration rights obligations contained in the Xxxx Petroleum/Xxxxxx Companies Acquisition Agreement dated June 9, 2008 by and between the Company and other subsidiaries of the Company and Xxxx Petroleum Corporation, Xxxxxx Xxxx Exploration Company and Xxxxxx Xxxx Production Company as provided in the Preliminary Prospectus).

(hh) There are no contracts or other documents which are required by the Rules and Regulations to be described in the most recent Preliminary Prospectus and Prospectus or filed as exhibits to the Registration Statement by the Securities Act or by the Rules and Regulations which have not been described in such Preliminary Prospectus and Prospectus or filed as exhibits to the Registration Statement.

(ii) No relationship, direct or indirect, exists between or among the Company on the one hand, and the directors, officers, stockholders, customers or suppliers of the Company on the other hand, which is required by the Rules and Regulations to be described in the most recent Preliminary Prospectus and Prospectus which is not so described.

(jj) The Company has filed all federal, state and local income and franchise tax returns required to be filed through the date hereof and has paid all taxes due thereon, and no tax deficiency has been determined adversely to the Company or any of its subsidiaries which has had (nor does the Company have any knowledge of any asserted tax deficiency which, if determined adversely to the Company or any of its subsidiaries, would have) a material adverse effect on the consolidated financial position, stockholders’ equity, results of operations, business or prospects of the Company and its subsidiaries.

(kk) There is and has been no failure on the part of the Company and any of the Company’s directors or officers, in their capacities as such, to comply with the provisions of the Xxxxxxxx-Xxxxx Act of 2002 and the rules and regulations promulgated in connection therewith.

(ll) The Company has not received any written comments from the Commission staff in connection with the Company’s reports under the Exchange Act that remain unresolved.

(mm) The Company has not distributed and, prior to the later to occur of the Delivery Date and completion of the distribution of the Notes, will not distribute any offering material in connection with the offering and sale of the Notes other than any Preliminary Prospectus, the Prospectus, any Issuer Free Writing Prospectus to which the Representatives have consented in accordance with Section 1(f) or 5(g).

Any certificate signed by any officer of the Company and delivered to the Representatives or counsel for the Underwriters in connection with the offering of the Notes shall be deemed a representation and warranty by the Company, as to matters covered thereby, to each Underwriter.

Section 2. Purchase of the Notes by the Underwriters. On the basis of the representations and warranties contained in, and subject to the terms and conditions of, this Agreement, the Company agrees to issue and sell to the several Underwriters, and each of the Underwriters, severally and not jointly, agrees to purchase from the Company, at a price equal to 99.688% of the principal amount of the 2010 Notes, at a price equal to 99.331% of the principal amount of the 2013 Notes, at a price equal to 99.063% of the principal amount of the 2018 Notes, and at a price equal to 93.516% of the principal amount of the 2037 Notes, in each case plus accrued interest, if any, from the Delivery Date (or, in the case of the 2037 Notes, from August 1, 2008), the principal amount of each of the 2010 Notes, 2013 Notes, 2018 Notes and 2037 Notes set forth opposite that Underwriter’s name in Schedule I hereto.

Section 3. Offering of Notes by the Underwriters. Upon authorization by the Company of the release of the Notes, the several Underwriters propose to offer the Notes for sale upon the terms and conditions set forth in the Prospectus.

Section 4. Delivery of and Payment for the Notes. Delivery of and payment for the Notes shall be made at the offices of Xxxxx, Xxxx & Xxxxxxx LLP, Fort Worth, Texas at 10:00 A.M., New York City time, on August 7, 2008, or at such other date or place as shall be determined by agreement between the Representatives and the Company. This date and time are sometimes referred to as the “Delivery Date.” On the Delivery Date, the Company shall deliver or cause to be delivered the Notes to the Representatives for the account of each Underwriter against payment by the several Underwriters through the Representatives of the respective aggregate purchase prices of the Notes being sold by the Company to or upon the order of the Company of the purchase price by wire transfer in immediately available funds to the accounts specified by the Company. Time shall be of the essence, and delivery at the time and place specified pursuant to this Agreement is a further condition of the obligation of each Underwriter hereunder.

Section 5. Further Agreements of the Company. The Company agrees:

(a) To prepare the Prospectus in a form approved by the Representatives and to file such Prospectus pursuant to Rule 424(b) under the Securities Act not later than the Commission’s close of business on the second business day following the execution and delivery of this Agreement; to make no further amendment or any supplement to the Registration Statement or the Prospectus prior to the Delivery Date except as provided herein; to prepare the Final Term Sheet, substantially in the form of Schedule III hereto and approved by the Representatives and file the Final Term Sheet pursuant to Rule 433(d) of the Rules and Regulations within the time period prescribed by such Rule; to advise the Representatives, promptly after it receives notice thereof, of the time when any amendment or supplement to the Registration Statement or the Prospectus has been filed and to furnish the Representatives with copies thereof; to file promptly all reports and any definitive proxy or information statements required to be filed by the Company with the Commission pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of the Prospectus and for so long as the delivery of a prospectus is required in connection with the offering or sale of the Notes; to advise the Representatives, promptly after it receives notice thereof, of the issuance by the Commission of any stop order or of any order preventing or suspending the use of the Preliminary Prospectus, Prospectus or any Issuer Free Writing Prospectus, of the suspension of the qualification of the Notes for offering or sale in any jurisdiction, of the initiation or threatening of any proceeding or examination for any such purpose, of any notice from the Commission objecting to the use of the form of the Registration Statement or any post-effective amendment thereto or of any request by the Commission for the amending or supplementing of the Registration Statement, Preliminary Prospectus or the Prospectus or any Issuer Free Writing Prospectus or for additional information; and, in the event of the issuance of any stop order or of any order preventing or suspending the use of the Preliminary Prospectus, Prospectus or any Issuer Free Writing Prospectus or suspending any such qualification, to use promptly its best efforts to obtain its withdrawal;

(b) To pay the applicable Commission filing fees relating to the Notes within the time required by Rule 456(b)(1) without regard to the proviso therein;

(c) To furnish promptly to each of the Representatives and to counsel for the Underwriters a signed copy of the Registration Statement as originally filed with the Commission, and each amendment thereto filed with the Commission, including all consents and exhibits filed therewith;

(d) To deliver promptly to the Representatives such number of the following documents as the Representatives shall reasonably request: (A) conformed copies of the Registration Statement as originally filed with the Commission and each amendment thereto (in each case excluding exhibits other than this Agreement and the computation of per share earnings), (B) each Preliminary Prospectus, the Prospectus and any amended or supplemented Prospectus, (C) each Issuer Free Writing Prospectus, (D) the Final Term Sheet, and (E) any document incorporated by reference in any Preliminary Prospectus or the Prospectus;

(e) During the period in which the Prospectus relating to the Notes (or in lieu thereof, the notice referred to in Rule 173(a) of the Rules and Regulations) is required to be delivered under the Securities Act, to comply with all requirements imposed upon it by the Securities Act and by the Rules and Regulations, as from time to time in force, so far as is necessary to permit the continuance of sales of or dealings in the Notes as contemplated by the provisions of this Agreement and by the Prospectus. If during such period any event occurs as a result of which the Pricing Disclosure Package or the Prospectus as then amended or supplemented would include an untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances then existing, not misleading, or if during such period it is necessary to amend the Registration Statement or amend or supplement the Pricing Disclosure Package or the Prospectus or file any document to comply with the Securities Act, the Company will promptly notify the Representatives and will, subject to Section 5(a) hereof, amend the Registration Statement, amend or supplement the Pricing Disclosure Package or the Prospectus, as the case may be, or file any document (in each case, at the expense of the Company) so as to correct such statement or omission or to effect such compliance, and will furnish without charge to each Underwriter as many written and electronic copies of any such amendment or supplement as the Representatives may from time to time reasonably request;

(f) To file promptly with the Commission any amendment or supplement to the Registration Statement or the Prospectus that may, in the judgment of the Company or the Representatives, be required by the Securities Act or requested by the Commission;

(g) For so long as the delivery of a prospectus is required in connection with the offering or sale of the Notes, prior to filing with the Commission any amendment or supplement to the Registration Statement or the Prospectus, any document incorporated by reference in the Prospectus or any amendment to any document incorporated by reference in the Prospectus, to furnish a copy thereof to the Representatives and counsel for the Underwriters and obtain the consent of the Representatives to the filing, which consent shall not be unreasonably withheld;

(h) Not to make any offer relating to the Notes that would constitute an Issuer Free Writing Prospectus without the prior written consent of the Representatives (which consent being deemed to have been given with respect to (A) the Final Term Sheet prepared and filed pursuant to Section 5(a) hereof and (B) any other Issuer Free Writing Prospectus identified on Schedule II hereto).

(i) To comply with all applicable requirements of Rule 433 with respect to any Issuer Free Writing Prospectus; and if at any time after the date hereof any events shall have occurred as a result of which any Issuer Free Writing Prospectus, as then amended or supplemented, would conflict with the information in the Registration Statement, the most recent Preliminary Prospectus or the Prospectus or would include an untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading, or, if for any other reason it shall be necessary to amend or supplement any Issuer Free Writing Prospectus, to notify the Representatives and, upon their request, to file such document and to prepare and furnish without charge to each Underwriter as many copies as the Representatives may from time to time reasonably request of an amended or supplemented Issuer Free Writing Prospectus that will correct such conflict, statement or omission or effect such compliance;

(j) Promptly from time to time to take such action as the Representatives may reasonably request to qualify the Notes for offering and sale under the securities laws of such other jurisdictions as the Representatives may request and to comply with such laws so as to permit the continuance of sales and dealings therein in such jurisdictions for as long as may be necessary to complete the distribution of the Notes; provided, that in connection therewith the Company shall not be required to (i) qualify as a foreign corporation in any jurisdiction in which it would not otherwise be required to so qualify, (ii) file a general consent to service of process in any such jurisdiction or (iii) subject itself to taxation in any jurisdiction in which it would not otherwise be subject;

(k) As soon as practicable after the Effective Date and in any event not later than 12 months after the date hereof, to make generally available to the Company’s security holders and to deliver to the Representatives an earnings statement of the Company and its subsidiaries (which need not be audited) complying with Section 11(a) of the Securities Act and the Rules and Regulations;

(l) To apply the net proceeds from the sale of the Notes being sold by the Company as set forth in the Prospectus;

(m) Not to take any action designed to or that might reasonably be expected to cause or result in the stabilization or manipulation of the price of the Notes to facilitate the sale or resale of the Notes;

(n) To take such steps as shall be necessary to ensure that neither the Company nor any subsidiary shall become an investment company as defined in the Investment Company Act;

(o) To file promptly all reports and any definitive proxy or information statements required to be filed by the Company with the Commission pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of the Prospectus and for so long as the delivery of a prospectus is required in connection with the offering or sale of the Notes;

(p) From the date hereof through the Delivery Date, the Company agrees not to, directly or indirectly, sell, offer to sell, contract to sell, grant any option to purchase, issue any instrument convertible into or exchangeable for, or otherwise transfer or dispose of (or enter into any transaction or device that is designed to, or could be expected to, result in the disposition by any person at any time in the future of) any debt securities of the Company with substantially similar terms to any of the 2010 Notes, 2013 Notes, 2018 Notes or 2037 Notes, except with the prior written consent of Xxxxxx Brothers Inc. and Banc of America Securities LLC; and

(q) To comply with all agreements set forth in the representation letters of the Company to DTC relating to the acceptance of the Notes for “book-entry” transfer through the facilities of DTC.

Section 6. Representation Warranty and Agreement of Underwriters. Each Underwriter represents and warrants to, and agrees with, the Company and each other Underwriter that it has not made, and will not make (other than one or more term sheets relating to the Notes containing customary information not inconsistent with the final term sheet prepared and filed pursuant to Section 5(a) hereof) any offer, relating to the Notes that would constitute a “free writing prospectus” (as defined in Rule 405 under the Securities Act) that would be required to be filed with the Commission pursuant to Rule 433 under the Securities Act, without the prior consent of the Company and the Representatives.

Section 7. Expenses. Whether or not this Agreement becomes effective or is terminated or the sale of the Notes to the Underwriters is consummated, the Company shall pay or cause to be paid (A) all fees, costs, expenses and taxes incident to the performance of its obligations under this Agreement, (including, without limitation, all registration and filing fees and fees and expenses of the Company’s accountants but excluding fees and expenses of counsel for the Underwriters) incurred in connection with the preparation, printing, filing, delivery and shipping of the Registration Statement (including the financial statements therein and all amendments, post-effective amendments and exhibits thereto), the Prospectus, the Indenture, the Statement of Eligibility and Qualification of the Trustee on Form T-1 filed with the Commission (the “Form T-1”), any “issuer free writing prospectus” (as defined in Rule 433 under the Securities Act), and any amendments or supplements of the foregoing and any documents incorporated by reference into any of the foregoing, (B) all fees and expenses incurred in connection with the preparation and delivery to the Underwriters of the Notes (including the cost of printing the Notes), (C) any fees required to be paid to rating agencies incurred in connection with the rating of the Notes, (D) the fees, costs and charges of the Trustee, including the fees and disbursements of counsel for the Trustee, and (E) all other costs and expenses incident to the performance of the obligations of the Company under this Agreement; provided, that except as provided in this Section 7 and in Section 12, the Underwriters shall pay their own costs and expenses, including the costs and expenses of their counsel, any transfer taxes on the Notes that they may sell and the expenses of tombstone advertising any offering of the Notes made by the Underwriters.

Section 8. Conditions of Underwriters’ Obligations. The respective obligations of the Underwriters hereunder are subject to the accuracy, as of the date hereof, as of the Applicable Time and the Delivery Date (as if made on the Delivery Date), of the representations and warranties of the Company contained herein, to the performance by the Company of its obligations hereunder, and to each of the following additional terms and conditions:

(a) The Prospectus shall have been timely filed with the Commission in accordance with Section 5(a); all filings (including, without limitation, the Final Term Sheet) required by Rule 424(b) or Rule 433 of the Rules and Regulations shall have been made within the time periods prescribed by such Rules, and no such filings will have been made without the consent of the Representatives; no stop order suspending the effectiveness of the Registration Statement or preventing, suspending the use of the Prospectus or any Issuer Free Writing Prospectus or suspending the qualification of the Notes for offering or sale in any jurisdiction shall have been issued and no proceeding or examination for such purpose shall have been initiated or threatened by the Commission; any request of the Commission for inclusion of additional information in the Registration Statement or the Prospectus or otherwise shall have been complied with; and the Commission shall not have notified the Company of any objection to the use of the form of the Registration Statement.

(b) No Underwriter shall have discovered and disclosed to the Company on or prior to the Delivery Date that the Registration Statement, the Pricing Disclosure Package or the Prospectus or any amendment or supplement thereto contains an untrue statement of a fact which, in the opinion of Xxxxxx & Xxxxxx L.L.P., counsel for the Underwriters, is material or omits to state a fact which, in the opinion of such counsel, is material and is required to be stated therein or is necessary to make the statements therein not misleading.

(c) All corporate proceedings and other legal matters incident to the authorization, form and validity of this Agreement, the Indenture, the Notes, the Registration Statement, the Prospectus and any Issuer Free Writing Prospectus, and all other legal matters relating to this Agreement and the transactions contemplated hereby shall be reasonably satisfactory in all material respects to counsel for the Underwriters, and the Company shall have furnished to such counsel all documents and information that they may reasonably request to enable them to pass upon such matters;

(d) Xxxxx, Xxxx & Xxxxxxx LLP shall have furnished to the Underwriters their written opinion, as counsel to the Company, addressed to the Underwriters and dated the Delivery Date, in form and substance reasonably satisfactory to the Underwriters, to the effect that:

(i) The Company was incorporated, exists and is in good standing under the laws of the State of Delaware, with the corporate power and authority to own its properties and conduct its business as described in the Prospectus;

(ii) The Company is qualified as a foreign corporation for the transaction of business and is in good standing in the State of Texas and each other state set forth on an exhibit to such opinion, and such counsel has no knowledge that the character of the business conducted

by the Company or the location of the properties owned, leased or operated by it makes such qualification necessary in any other state (except where the failure to so qualify would not, individually or in the aggregate, have a material adverse effect on the condition (financial or other), results of operations, business or prospects of the Company and its subsidiaries taken as a whole);

(iii) Each subsidiary of the Company was organized, exists and is in good standing under the laws of its jurisdiction of formation; all of the issued shares of capital stock or other equity interests of each such subsidiary have been validly authorized and issued, are fully paid and non-assessable (in the case of capital stock of a corporation), and are owned of record by the Company directly or through subsidiaries, and such counsel has no knowledge of any adverse claim (within the meaning of Article 8 of the Uniform Commercial Code) thereto;

(iv) The Registration Statement became effective under the Securities Act on the date it was filed with the Commission; the Preliminary Prospectus was filed with the Commission on August 4, 2008 pursuant to Rule 424(b) of the Rules and Regulations; the Prospectus to be filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations; and such counsel has no knowledge after due inquiry of the issuance of any stop order suspending the effectiveness of the Registration Statement, or preventing or suspending the use of the Preliminary Prospectus, the Prospectus or any Issuer Free Writing Prospectus, or of any proceeding for that purpose that is pending or threatened by the Commission;

(v) Such counsel has no knowledge that the filing of the Registration Statement or the offering or sale of the Notes as contemplated by this Agreement would give rise to any rights, other than those which have been waived or satisfied or which arise under the 1993 Registration Rights Agreement, for or relating to the registration of any securities of the Company or any of its subsidiaries. The Company has all requisite corporate power and authority to issue, sell and deliver the Notes in accordance with and upon the terms and conditions set forth in this Agreement and in the Indenture, the Registration Statement, the Preliminary Prospectus and the Prospectus;

(vi) The Indenture has been duly authorized, executed and delivered by the Company and, assuming the due authorization, execution and delivery by the Trustee, is a valid and binding agreement of the Company, enforceable against the Company in accordance with its terms, except as the enforceability thereof may be limited by bankruptcy, insolvency, reorganization, moratorium or similar laws relating to or affecting creditors’ rights generally and by general equitable principles (regardless of whether such enforceability is considered in a proceeding in equity or at law); and the Indenture conforms in all material respects with the requirements of the Trust Indenture Act and the Rules and Regulations applicable to an indenture that is qualified thereunder;

(vii) The Notes have been duly authorized and executed by the Company for issuance and sale to the Underwriters pursuant to this Agreement and, assuming due authentication of the Notes by the Trustee, upon delivery to the Underwriters against payment therefor in accordance with the terms of this Agreement, will have been validly issued and

delivered, will be entitled to the benefits of the Indenture and will constitute valid and binding obligations of the Company, enforceable against the Company in accordance with their terms, except as enforcement thereof may be limited by bankruptcy, insolvency, reorganization, moratorium or other similar laws or judicial decisions relating to or affecting creditors’ rights generally and by general equitable principles (regardless of whether such enforceability is considered in a proceeding in equity or at law);

(viii) Such counsel has no knowledge, other than as set forth in the Preliminary Prospectus and the Prospectus, of any pending or overtly threatened legal or governmental proceedings to which the Company or any of its subsidiaries is or may be a party or of which any property of the Company or any of its subsidiaries is or may be subject which, if determined adversely to the Company or any of its subsidiaries would, individually or in the aggregate, have a material adverse effect on the consolidated financial position, equity or results of operations of the Company and its subsidiaries;

(ix) This Agreement has been duly authorized, executed and delivered by the Company;

(x) The issue and sale of the Notes being delivered on the Delivery Date by the Company and the compliance by the Company with all of its obligations under this Agreement and the Indenture and consummation of the transactions contemplated hereby and thereby will not (A) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, the Indenture or any other indenture, mortgage, deed of trust, loan agreement, license or other agreement or instrument (other than the 1993 Registration Rights Agreement as to which counsel need not opine) known to such counsel to which the Company or any of its subsidiaries is a party or by which the Company or any of its subsidiaries is bound or to which any of the property or assets of the Company or any of its subsidiaries is subject, (B) impose any lien, charge or encumbrance upon any property or assets of the Company and its subsidiaries known to such counsel, (C) violate any provisions of the Restated Certificate of Incorporation or Bylaws of the Company or (D) violate any statute, rule or regulation known to such counsel (excluding any securities or anti-fraud statute, rule or regulation), or any order known to such counsel of any court or governmental agency or body having jurisdiction over the Company or any of its subsidiaries or any of their properties or assets; and, except for the registration of the Notes under the Securities Act, the qualification of the Indenture and the Indenture trustee under the Trust Indenture Act and such consents, approvals, authorizations, registrations or qualifications as may be required under the Exchange Act and applicable state or foreign securities laws in connection with the purchase and distribution of the Notes by the Underwriters, no consent, approval, authorization or order of, or filing or registration with, any such court or governmental agency or body having jurisdiction over the Company and any of its subsidiaries or any of their properties or assets is required for the execution, delivery and performance of this Agreement by the Company and the purchase and distribution of such Notes by the Underwriters;

(xi) Such counsel has no knowledge that (i) the Company is in violation of its Restated Certificate of Incorporation or Bylaws, or (ii) any of the Company’s subsidiaries is in

violation of its charter or bylaws or other governing documents or (iii) the Company or any of its subsidiaries is in default in the performance or observance of any material obligation, agreement, covenant or condition contained in any indenture, mortgage, deed of trust, loan agreement, lease or other agreement or instrument (other than the 1993 Registration Rights Agreement as to which counsel need not opine) known to such counsel to which it is a party or by which it or any of its properties may be bound;

(xii) The statements set forth in the Preliminary Prospectus and the Prospectus under the captions “Description of Other Indebtedness,” “Description of the Notes,” “Description of Senior Debt Securities,” and “Certain United States Federal Income Tax Considerations,” insofar as they constitute matters of law, summaries of legal matters, documents or legal conclusions, have been reviewed by such counsel and are correct in all material respects;

(xiii) The Company is not, and after giving effect to the sale of the Notes to the Underwriters as contemplated by this Agreement and the application of the proceeds therefrom will not be, an “investment company” as such term is defined in the Investment Company Act of 1940, as amended;

(xiv) Such counsel has no knowledge of any contracts or other documents that are required by the Securities Act or by the Rules and Regulations to be described in the Registration Statement or the most recent Preliminary Prospectus or filed as exhibits to the Registration Statement which have not been so described or filed;

(xv) (A) The Registration Statement, on the latest Effective Date and on the Delivery Date, and (B) the Preliminary Prospectus and the Prospectus, when filed with the Commission pursuant to Rule 424(b) and on the Delivery Date, and any further amendments and supplements thereto made by the Company prior to the Delivery Date (other than the financial statements, notes thereto and related schedules therein, and the information pertaining to oil and gas reserves and related data, and the financial data that is included therein, as to which such counsel expresses no opinion) comply as to form in all material respects with the requirements of the Securities Act and the Rules and Regulations; and

(xvi) The documents incorporated by reference in the Prospectus and the Registration Statement (other than the financial statements, notes thereto and related schedules therein, and the information pertaining to oil and gas reserves and related data, and other financial data that is included therein, as to which such counsel need express no opinion), when filed with the Commission, complied as to form in all material respects with the requirements of the Exchange Act and the rules and regulations of the Commission thereunder.

In addition to the opinions set forth above, such opinion shall also include a statement to the effect that although such counsel does not assume any responsibility for the accuracy, completeness or fairness of the statements contained in the Registration Statement, the Prospectus or any further amendment or supplement thereto, except for those referred to in the opinion in subsection (xii) above, nothing has come to the attention of such counsel that has caused them to believe that, (A) as of the latest Effective Time, the Registration Statement, or

any further amendment thereto prior to the Delivery Date (other than the financial statements, notes thereto and related schedules therein, the information pertaining to oil and gas reserves and related data, and other financial data that is included therein, as to which such counsel need express no opinion) contained an untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (B) as of its date and as of the Delivery Date, the Prospectus or any further amendment or supplement thereto prior to the Delivery Date (other than the financial statements, notes thereto and related schedules therein, the information pertaining to oil and gas reserves and related data, and other financial data that is included therein, as to which such counsel need express no opinion) contained an untrue statement of a material fact or omitted to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, or (C) as of the Applicable Time, the most recent Preliminary Prospectus, together with the information included on Schedule III hereto and the Issuer Free Writing Prospectuses set forth on a schedule to such opinion (other than the financial statements, notes thereto and related schedules therein, the information pertaining to oil and gas reserves and related data, and other financial data that is included therein, as to which such counsel need express no opinion), contains an untrue statement of a material fact or omits to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; and such counsel does not know of any amendment to the Registration Statement required to be filed or of any contracts or other documents of a character required to be filed as an exhibit to the Registration Statement or required to be described in the Registration Statement, the Preliminary Prospectus or the Prospectus which are not filed or described as required;

(e) The Representatives shall have received from Xxxxxx & Xxxxxx L.L.P., counsel for the Underwriters, such opinion or opinions, dated the Delivery Date, with respect to the issuance and sale of the Notes, the Registration Statement, the Pricing Disclosure Package, the Prospectus and other related matters as the Representatives may reasonably require, and the Company shall have furnished to such counsel such documents as they reasonably request for the purpose of enabling them to pass upon such matters.

(f) At the time of execution of this Agreement, the Representatives shall have received from KPMG a letter (the “initial letter”), in form and substance reasonably satisfactory to the Underwriters, addressed to the Underwriters and dated the date hereof (i) confirming that, with respect to the Company, they are independent public accountants within the meaning of the Securities Act and are in compliance with the applicable requirements relating to the qualification of accountants under Rule 2-01 of Regulation S-X of the Commission and (ii) stating, as of the date hereof (or, with respect to matters involving changes or developments since the respective dates as of which specified financial information is given in the most recent Preliminary Prospectus and the Prospectus, as of a date not more than three days prior to the date hereof), the conclusions and findings of such firm with respect to the financial information and other matters ordinarily covered by accountants’ “comfort letters” to underwriters in connection with registered public offerings.

(g) With respect to the letter of KPMG referred to in the preceding paragraph and delivered to the Representatives concurrently with the execution of this Agreement, the Company shall have furnished to the Representatives a letter (the “bring-down letter”) of such accountants, addressed to the Underwriters and dated the Delivery Date (i) confirming that they are independent public accountants within the meaning of the Securities Act and are in compliance with the applicable requirements relating to the qualification of accountants under Rule 2-01 of Regulation S-X of the Commission, (ii) stating, as of the date of the bring-down letter (or, with respect to matters involving changes or developments since the respective dates as of which specified financial information is given in the Prospectus, as of a date not more than three days prior to the date of the bring-down letter), the conclusions and findings of such firm with respect to the financial information and other matters covered by the initial letter and (iii) confirming in all material respects the conclusions and findings set forth in the initial letter.

(h) The Company shall have furnished to the Representatives a certificate, dated the Delivery Date, of its Chairman of the Board, its President or a Vice President and its chief financial officer stating that:

(i) The representations, warranties and agreements of the Company in Section 1 are true and correct on and as of the Delivery Date; the Company has complied with all its agreements contained herein and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to the Delivery Date;

(ii) No stop order suspending the effectiveness of the Registration Statement has been issued; no proceedings or examination for that purpose have been instituted or, to the knowledge of such officers, threatened; and the Commission has not notified the Company of any objection to the use of the form of the Registration Statement or any post-effective amendment thereto; and

(iii) They have carefully examined the Registration Statement, the Prospectus and the Pricing Disclosure Package and, in their opinion, (A) (1) the Registration Statement, as of the Effective Date, (2) the Prospectus, as of its date and on the Delivery Date, or (3) the Pricing Disclosure Package, as of the Applicable Time, did not and do not contain any untrue statement of a material fact and did not and do not omit to state a material fact required to be stated therein or necessary to make the statements therein (except in the case of the Registration Statement, in the light of the circumstances under which they were made) not misleading, and (B) since the Effective Date, no event has occurred that is required by the Rules and Regulations to be set forth in a supplement or amendment to the Registration Statement, the Pricing Disclosure Package, the Prospectus or any Issuer Free Writing Prospectus that has not been so set forth.

(i) Neither the Company nor any of its subsidiaries shall have sustained since the date of the latest audited financial statements included or incorporated by reference in the Prospectus (exclusive of any amendment or supplement thereto on or after the date of this Agreement) (i) any loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor dispute or court or governmental action, order or

decree, otherwise than as set forth or contemplated in the Prospectus or (ii) since such date there shall not have been any change in the capitalization or long-term debt of the Company or any of its subsidiaries, other than changes to indebtedness outstanding under the Company’s Term Loan Agreement dated November 10, 2004, as amended, between the Company and Bank of America, as Administrative Agent, and other lenders, the Company’s Term Loan Agreement dated February 5, 2008 between the Company and the Royal Bank of Scotland Finance (Ireland), the Company’s Amended and Restated 5-Year Revolving Credit Agreement, dated April 1, 2005 between the Company and certain commercial banks named therein, as amended to date, and the Company’s commercial paper program, or any change, or any development involving a prospective change, in or affecting the general affairs, management, financial position, stockholders’ equity or results of operations of the Company and its subsidiaries, otherwise than as set forth or contemplated in the Preliminary Prospectus, the effect of which, in any such case described in clause (i) or (ii), is, in the judgment of the Representatives, so material and adverse as to make it impracticable or inadvisable to proceed with the public offering or the delivery of the Notes being delivered on the Delivery Date on the terms and in the manner contemplated in the Preliminary Prospectus and the Prospectus.

(j) Subsequent to the execution and delivery of this Agreement there shall not have occurred any of the following: (i) trading in securities generally on the New York Stock Exchange or the American Stock Exchange or in the over-the-counter market, or trading in any securities of the Company on any exchange or in the over-the-counter market, shall have been suspended or materially limited or the settlement of such trading generally shall have been materially disrupted, or minimum prices shall have been established on any such exchange or such market by the Commission, by such exchange or by any other regulatory body or governmental authority having jurisdiction, (ii) a banking moratorium shall have been declared by federal or state authorities, (iii) a material disruption in clearance or settlement systems shall have occurred, (iv) the United States shall have become engaged in hostilities, there shall have been an escalation in hostilities involving the United States or there shall have been a declaration of a national emergency or war by the United States or (iv) there shall have occurred such a material adverse change in general economic, political or financial conditions (or the effect of international conditions on the financial markets in the United States shall be such), including, without limitation, as a result of terrorist activities or other calamity or crisis, after the date hereof, as to make it, in the judgment of the Representatives, impracticable or inadvisable to proceed with the public offering or delivery of the Notes being delivered on the Delivery Date on the terms and in the manner contemplated in the Preliminary Prospectus and the Prospectus.

(k) At the time of execution of this Agreement, the Representatives shall have received from Xxxxxx and Xxxxx, Ltd., independent petroleum engineers, an initial letter (the “initial expert letter”), in form and substance reasonably satisfactory to the Representatives and their counsel, addressed to the Underwriters and dated the date hereof and a subsequent letter dated as of the Delivery Date, which such letter shall cover the period from any initial expert letter to the Delivery Date, confirming that, with respect to the Company, they are independent petroleum engineers, and confirming such information related to the proved reserves of the Company as counsel to the Underwriters shall reasonably request.

(l) Subsequent to the execution and delivery of this Agreement, (i) no downgrading shall have occurred in the rating accorded the Notes or any other debt securities issued or guaranteed by the Company by either Standard & Poor’s, a division of The XxXxxx-Xxxx Companies, Inc. or Xxxxx’x Investors Service, Inc., or their respective successors; and (ii) neither such organization shall have publicly announced that it has under surveillance or review (other than an announcement with positive implications of a possible upgrading) its rating of the Notes or any other debt securities issued or guaranteed by the Company.

(m) On the Delivery Date, neither KPMG’s initial letter nor its bring-down letter shall have been rescinded and the Company shall have no reason to believe that the representations in such letter are not true and correct in all respects.

(n) On the Delivery Date, the Xxxxxx and Xxxxx Letter shall not have been rescinded and the Company shall have no reason to believe that the representations in such letter are not true and correct in all respects.

All opinions, letters, evidence and certificates mentioned above or elsewhere in this Agreement shall be deemed to be in compliance with the provisions hereof only if they are in form and substance reasonably satisfactory to counsel for the Underwriters.

Section 9. Indemnification and Contribution.

(a) The Company shall indemnify and hold harmless each Underwriter, its directors, officers and employees and each person, if any, who controls any Underwriter within the meaning of the Securities Act, from and against any loss, claim, damage or liability, joint or several, or any action in respect thereof (including, but not limited to, any loss, claim, damage, liability or action relating to purchases and sales of Notes), to which that Underwriter, director, officer, employee or controlling person may become subject, under the Securities Act or otherwise, insofar as such loss, claim, damage, liability or action arises out of, or is based upon, (i) any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement, the Preliminary Prospectus, the Prospectus, any other preliminary prospectus supplement relating to the Notes, any other prospectus relating to the Notes or included in the Registration Statement, any amendment or supplement to any of the foregoing, any Permitted Free Writing Prospectus, any “issuer free writing prospectus” (as defined in Rule 433 under the Securities Act), being hereinafter referred to as an “Issuer Free Writing Prospectus”, any “issuer information” filed or required to be filed pursuant to Rule 433(d), or any road show that does not otherwise constitute an Issuer Free Writing Prospectus, including any road show or investor presentations made to investors by the Company (whether in person or electronically), or any omission or alleged omission to state therein any material fact required to be stated therein or necessary to make the statements therein not misleading or (ii) any act or failure to act or any alleged act or failure to act by any Underwriter in connection with, or relating in any manner to, the Notes or the offering contemplated hereby, and which is included as part of or referred to in any loss, claim, damage, liability or action arising out of or based upon matters covered by clause (i) above (provided, that the Company shall not be liable under this clause (ii) to the extent that it is determined in a final judgment by a court of competent jurisdiction that

such loss, claim, damage, liability or action resulted directly from any such acts or failures to act undertaken or omitted to be taken by such Underwriter through its gross negligence or willful misconduct), and, in each case, shall reimburse each Underwriter and each such director, officer, employee or controlling person promptly upon demand for any legal or other expenses reasonably incurred by that Underwriter, director, officer, employee or controlling person in connection with investigating or defending or preparing to defend against any such loss, claim, damage, liability or action as such expenses are incurred; provided, however, that the Company shall not be liable in any such case to the extent that any such loss, claim, damage, liability or action arises out of, or is based upon, any untrue statement or alleged untrue statement or omission or alleged omission made in the Prospectus, the Registration Statement, the Preliminary Prospectus, the Prospectus as amended and supplemented or any Issuer Free Writing Prospectus, or in any such amendment or supplement, in reliance upon and in conformity with written information concerning such Underwriter furnished to the Company through the Representatives by or on behalf of any Underwriter specifically for inclusion therein which information consists solely of the information specified in Section 9(e). The obligations of the Company under this Section shall be in addition to any liability which the Company may otherwise have and shall extend, upon the same terms and conditions, to each person, if any, who controls any Underwriter within the meaning of the Securities Act; and the obligations of the Underwriters under this Section shall be in addition to any liability which the respective Underwriters may otherwise have and shall extend, upon the same terms and conditions, to each director of the Company, to each officer of the Company who has signed a Registration Statement and to each person, if any, who controls the Company within the meaning of the Securities Act.

(b) Each Underwriter, severally and not jointly, shall indemnify and hold harmless the Company, its directors, officers and employees, and each person, if any, who controls the Company within the meaning of Section 15 of the Securities Act, from and against any loss, claim, damage or liability, joint or several, or any action in respect thereof, to which the Company or any such director, officer, employee or controlling person may become subject, under the Securities Act or otherwise, insofar as such loss, claim, damage, liability or action arises out of, or is based upon, any untrue statement or alleged untrue statement of a material fact contained in any Registration Statement, the Preliminary Prospectus, the Prospectus, any other preliminary prospectus supplement relating to the Notes, any other prospectus relating to the Notes or included in the Registration Statement, any amendment or supplement to any of the foregoing, any Permitted Free Writing Prospectus, any Issuer Free Writing Prospectus, any “issuer information” filed or required to be filed pursuant to Rule 433(d), or any road show that does not otherwise constitute an Issuer Free Writing Prospectus, including any road show or investor presentations made to investors by the Company (whether in person or electronically), or any omission or alleged omission to state therein any material fact required to be stated therein or necessary to make the statements therein not misleading, but in each case only to the extent that the untrue statement or alleged untrue statement or omission or alleged omission was made in reliance upon and in conformity with written information concerning such Underwriter furnished to the Company through the Representatives by or on behalf of that Underwriter specifically for inclusion therein (which information is limited to the information set forth in Section 9(e)), and shall reimburse the Company and each such director, officer, employee or controlling person

promptly upon demand for any legal or other expenses reasonably incurred by the Company or any such director, officer, employee or controlling person in connection with investigating or defending or preparing to defend against any such loss, claim, damage, liability or action as such expenses are incurred. The foregoing indemnity agreement is in addition to any liability that any Underwriter may otherwise have to the Company or any such director, officer, employee or controlling person.

(c) Promptly after receipt by an indemnified party under this Section 9 of notice of any claim or the commencement of any action, the indemnified party shall, if a claim in respect thereof is to be made against the indemnifying party under this Section 9, notify the indemnifying party in writing of the claim or the commencement of that action; provided, however, that the failure to notify the indemnifying party shall not relieve it from any liability which it may have under this Section 9 except to the extent it has been materially prejudiced by such failure and, provided further, that the failure to notify the indemnifying party shall not relieve it from any liability which it may have to an indemnified party otherwise than under this Section 9. If any such claim or action shall be brought against an indemnified party, and it shall notify the indemnifying party thereof, the indemnifying party shall be entitled to participate therein and, to the extent that it wishes, jointly with any other similarly notified indemnifying party, to assume the defense thereof with counsel reasonably satisfactory to the indemnified party. After notice from the indemnifying party to the indemnified party of its election to assume the defense of such claim or action, the indemnifying party shall not be liable to the indemnified party under this Section 9 for any legal or other expenses subsequently incurred by the indemnified party in connection with the defense thereof other than reasonable costs of investigation; provided, however, that the indemnified party shall have the right to employ counsel to represent jointly the indemnified party and their respective officers, employees and controlling persons who may be subject to liability arising out of any claim in respect of which indemnity may be sought by the Underwriters against the Company under this Section 9 if, in the reasonable judgment of the Representatives, it is advisable for the Underwriters, officers, employees and controlling persons to be jointly represented by separate counsel, and in that event the fees and expenses of one such separate counsel shall be paid by the Company. No indemnifying party shall (i) without the prior written consent of the indemnified parties (which consent shall not be unreasonably withheld), settle or compromise or consent to the entry of any judgment with respect to any pending or threatened claim, action, suit or proceeding in respect of which indemnification or contribution may be sought hereunder (whether or not the indemnified parties are actual or potential parties to such claim or action) unless such settlement, compromise or consent includes an unconditional release of each indemnified party from all liability arising out of such claim, action, suit or proceeding, or (ii) be liable for any settlement of any such action effected without its written consent (which consent shall not be unreasonably withheld), but if settled with the consent of the indemnifying party or if there be a final judgment of the plaintiff in any such action, the indemnifying party agrees to indemnify and hold harmless any indemnified party from and against any loss or liability by reason of such settlement or judgment.

(d) If the indemnification provided for in this Section 9 shall for any reason be unavailable to or insufficient to hold harmless an indemnified party under Section 9(a) or 9(b) in respect of any loss, claim, damage or liability, or any action in respect thereof, referred to therein,

then each indemnifying party shall, in lieu of indemnifying such indemnified party, contribute to the amount paid or payable by such indemnified party as a result of such loss, claim, damage or liability, or action in respect thereof, (i) in such proportion as shall be appropriate to reflect the relative benefits received by the Company on the one hand and the Underwriters on the other from the offering of the Notes or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the Company on the one hand and the Underwriters on the other with respect to the statements or omissions which resulted in such loss, claim, damage or liability, or action in respect thereof, as well as any other relevant equitable considerations. The relative benefits received by the Company on the one hand and the Underwriters on the other with respect to such offering shall be deemed to be in the same proportion as the total net proceeds from the offering of the Notes purchased under this Agreement (before deducting expenses) received by the Company on the one hand, and the total underwriting discounts and commissions received by the Underwriters with respect to the Notes purchased under this Agreement, on the other hand, bear to the total gross proceeds from the offering of the Notes under this Agreement, in each case as set forth in the table on the cover page of the Prospectus. The relative fault shall be determined by reference to whether the untrue or alleged untrue statement of a material fact or omission or alleged omission to state a material fact relates to information supplied by the Company or the Underwriters, the intent of the parties and their relative knowledge, access to information and opportunity to correct or prevent such statement or omission. The Company and the Underwriters agree that it would not be just and equitable if contributions pursuant to this Section were to be determined by pro rata allocation (even if the Underwriters were treated as one entity for such purpose) or by any other method of allocation which does not take into account the equitable considerations referred to herein. The amount paid or payable by an indemnified party as a result of the loss, claim, damage or liability, or action in respect thereof, referred to above in this Section shall be deemed to include, for purposes of this Section 9(d), any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any such action or claim. Notwithstanding the provisions of this Section 9(d), no Underwriter shall be required to contribute any amount in excess of the amount by which the total price at which the Notes underwritten by it and offered to the public exceeds the amount of any damages which such Underwriter has otherwise paid or become liable to pay by reason of any untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters’ obligations to contribute as provided in this Section 9(d) are several in proportion to their respective underwriting obligations and not joint.

(e) The Underwriters severally confirm and the Company acknowledges and agrees that the statements with respect to the public offering of the Notes by the Underwriters set forth in the final sentence on the cover page of the most recent Preliminary Prospectus, and the statements under the caption “Underwriting” in the most recent Preliminary Prospectus in the first paragraph under the subcaption “Commissions and Expenses,” the two paragraphs under the subcaption “Stabilization, Short Positions and Penalty Bids,” and the second sentence of the

paragraph under the subcaption “Trading Market,” in the most recent Preliminary Prospectus and the Prospectus constitute the only information concerning such Underwriters furnished in writing to the Company by or on behalf of the Underwriters specifically for inclusion in any Preliminary Prospectus, the Registration Statement, the Prospectus, any Issuer Free Writing Prospectus or in any amendment or supplement thereto.

Section 10. Defaulting Underwriters. If, on the Delivery Date, any Underwriter defaults in the performance of its obligations under this Agreement, the remaining non-defaulting Underwriters shall be obligated to purchase the principal amount of Notes that the defaulting Underwriter agreed but failed to purchase on the Delivery Date in the respective proportions which the principal amount of Notes set forth opposite the name of each remaining non-defaulting Underwriter in Schedule I hereto bears to the total principal amount of Notes that set forth opposite the names of all the remaining non-defaulting Underwriters in Schedule I hereto; provided, however, that the remaining non-defaulting Underwriters shall not be obligated to purchase any of the Notes on the Delivery Date if the total principal amount of Notes that the defaulting Underwriter or Underwriters agreed but failed to purchase on such date exceeds 9.09% of the total principal amount of Notes to be purchased on the Delivery Date, and any remaining non-defaulting Underwriter shall not be obligated to purchase more than 110% of the principal amount of Notes that it agreed to purchase on the Delivery Date pursuant to the terms of Section 2. If the foregoing maximums are exceeded, the remaining non-defaulting Underwriters, or those other underwriters satisfactory to the Representatives who so agree, shall have the right, but shall not be obligated, to purchase, in such proportion as may be agreed upon among them, all the Notes to be purchased on the Delivery Date. If the remaining Underwriters or other underwriters satisfactory to the Representatives do not elect to purchase the Notes that the defaulting Underwriter or Underwriters agreed but failed to purchase on the Delivery Date, this Agreement shall terminate without liability on the part of any non-defaulting Underwriter or the Company, except that the Company will continue to be liable for the payment of expenses to the extent set forth in Sections 7 and 12. As used in this Agreement, the term “Underwriter” includes, for all purposes of this Agreement unless the context requires otherwise, any party not listed in Schedule I hereto who, pursuant to this Section 10, purchases Notes that a defaulting Underwriter agreed but failed to purchase.

Nothing contained herein shall relieve a defaulting Underwriter of any liability it may have to the Company for damages caused by its default. If other underwriters are obligated or agree to purchase the Notes of a defaulting or withdrawing Underwriter, either the Representatives or the Company may postpone the Delivery Date for up to seven full business days in order to effect any changes that in the opinion of counsel for the Company or counsel for the Underwriters may be necessary in the Registration Statement, the Prospectus Supplement or in any other document or arrangement.

Section 11. Termination. The obligations of the Underwriters hereunder may be terminated by the Representatives by notice given to and received by the Company prior to delivery of and payment for the Stock if, prior to that time, any of the events described in Sections 8(i), 8(j) or 8(l) shall have occurred or if the Representatives shall decline to purchase the Notes for any reason permitted under this Agreement.

Section 12. Reimbursement of Underwriters’ Expense. If the Company shall fail to tender the Notes for delivery to the Underwriters by reason of any failure, refusal or inability on the part of the Company to perform any agreement on its part to be performed, or because any other condition of the Underwriters’ obligations hereunder required to be fulfilled by the Company is not fulfilled, the Company will reimburse the Underwriters for all reasonable out-of-pocket expenses (including fees and disbursements of counsel) incurred by the Underwriters in connection with this Agreement and the proposed purchase of the Notes, and upon demand the Company shall pay the full amount thereof to the Representatives. If this Agreement is terminated pursuant to Section 10 by reason of the default of one or more Underwriters, the Company shall not be obligated to reimburse any defaulting Underwriter on account of those expenses.

Section 13. Notices, Etc. All statements, requests, notices and agreements hereunder shall be in writing, and:

(a) if to the Underwriters, shall be delivered or sent by mail or facsimile transmission to Xxxxxx Brothers Inc., 000 Xxxxxxx Xxxxxx, Xxx Xxxx, Xxx Xxxx 00000, Attention: Debt Capital Markets, Power Group (Fax: (000) 000-0000), with a copy, in the case of any notice pursuant to Section 9(c), to the Director of Litigation, Office of the General Counsel, Xxxxxx Brothers Inc., 000 Xxxx Xxxxxx, 00^xx Xxxxx, Xxx Xxxx, Xxx Xxxx 00000; and

(b) if to the Company, shall be delivered or sent by mail, telex or facsimile transmission to the address of the Company set forth in the Registration Statement, Attention: Chief Financial Officer (Fax: (000) 000-0000). Any such statements, requests, notices or agreements shall take effect at the time of receipt thereof. The Company shall be entitled to act and rely upon any request, consent, notice or agreement given or made on behalf of the Underwriters by Xxxxxx Brothers Inc. on behalf of the Underwriters.

Section 14. Persons Entitled to Benefit of Agreement. This Agreement shall inure to the benefit of and be binding upon the Underwriters, the Company, and their respective successors. This Agreement and the terms and provisions hereof are for the sole benefit of only those persons, except that (A) the representations, warranties, indemnities and agreements of the Company contained in this Agreement shall also be deemed to be for the benefit of the directors, officers and employees of any Underwriter and the person or persons, if any, who control any Underwriter within the meaning of Section 15 of the Securities Act and (B) the indemnity agreement of the Underwriters contained in Section 9(b) of this Agreement shall be deemed to be for the benefit of directors of the Company, officers of the Company who have signed the Registration Statement and any person controlling the Company within the meaning of Section 15 of the Securities Act. Nothing in this Agreement is intended or shall be construed to give any person, other than the persons referred to in this Section 14, any legal or equitable right, remedy or claim under or in respect of this Agreement or any provision contained herein.

Section 15. Research Independence. The Company acknowledges that the Underwriters’ research analysts and research departments are required to be independent from their respective investment banking divisions and are subject to certain regulations and internal

policies, and that such Underwriters’ research analysts may hold views and make statements or investment recommendations and/or publish research reports with respect to the Company and/or the offering of the Notes that differ from the views of their respective investment banking divisions. The Company hereby waives and releases, to the fullest extent permitted by law, any claims that the Company may have against the Underwriters with respect to any conflict of interest that may arise from the fact that the views expressed by their independent research analysts and research departments may be different from or inconsistent with the views or advice communicated to the Company by such Underwriters’ investment banking divisions. The Company acknowledges that each of the Underwriters is a full service securities firm and as such from time to time, subject to applicable securities laws, may effect transactions for its own account or the account of its customers and hold long or short positions in debt or equity securities of the companies that may be the subject of the transactions contemplated by this Agreement.

Section 16. No Fiduciary Duty. The Company acknowledges and agrees that in connection with this offering, sale of the Notes or any other services the Underwriters may be deemed to be providing hereunder, notwithstanding any preexisting relationship, advisory or otherwise, between the parties or any oral representations or assurances previously or subsequently made by the Underwriters: (i) no fiduciary or agency relationship between the Company and any other person, on the one hand, and the Underwriters, on the other, exists; (ii) the Underwriters are not acting as advisors, expert or otherwise, to the Company, including, without limitation, with respect to the determination of the public offering price of the Notes, and such relationship between the Company, on the one hand, and the Underwriters, on the other, is entirely and solely commercial, based on arms-length negotiations; (iii) any duties and obligations that the Underwriters may have to the Company shall be limited to those duties and obligations specifically stated herein; and (iv) the Underwriters and their respective affiliates may have interests that differ from those of the Company. The Company hereby waives any claims that the Company may have against the Underwriters with respect to any breach of fiduciary duty in connection with this offering.

Section 17. Survival. The respective indemnities, representations, warranties and agreements of the Company and the Underwriters contained in this Agreement or made by or on behalf of them, respectively, pursuant to this Agreement, shall survive the delivery of and payment for the Notes and shall remain in full force and effect, regardless of any investigation made by or on behalf of any of them or any person controlling any of them.

Section 18. Definition of the Terms Business Day and Subsidiary. For purposes of this Agreement, (a) “business day” means each Monday, Tuesday, Wednesday, Thursday or Friday which is not a day on which banking institutions in New York are generally authorized or obligated by law or executive order to close and (b) “subsidiary” has the meaning set forth in Rule 405 of the Rules and Regulations.

Section 19. Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of New York.

Section 20. Counterparts. This Agreement may be executed in one or more counterparts and, if executed in more than one counterpart, the executed counterparts shall each be deemed to be an original but all such counterparts shall together constitute one and the same instrument.

Section 21. Headings. The headings herein are inserted for convenience of reference only and are not intended to be part of, or to affect the meaning or interpretation of, this Agreement.

If the foregoing correctly sets forth the agreement among the Company and the Underwriters, please indicate your acceptance in the space provided for that purpose below.


Very truly yours,

XTO ENERGY INC.

By:
	Name:	Xxxxx X. XxXxxxxx
	Title:	Senior Vice President

Accepted:

XXXXXX BROTHERS INC.

BANC OF AMERICA SECURITIES LLC

as Representatives of the Underwriters

set forth on Schedule I hereto


By:		XXXXXX BROTHERS INC.

By:
		Authorized Representative

UNDERWRITING AGREEMENT

SIGNATURE PAGE

SCHEDULE I


Underwriters	Amount of 2010 Notes to be Purchased		Amount of 2013 Notes to be Purchased		Amount of 2018 Notes to be Purchased		Amount of 2037 Notes to be Purchased
Xxxxxx Brothers Inc.		75,000,000		150,050,000		298,554,000		149,950,000
Banc of America Securities LLC		25,000,000		50,000,000		100,000,000		50,000,000
Xxxxxxxxx & Company, Inc.		45,000,000		15,742,000		47,976,000		13,350,000
Wachovia Capital Markets, LLC		45,014,000		15,742,000		47,976,000		13,350,000
BNP Paribas Securities Corp.		2,500,000		72,760,000		26,000,000		5,150,000
SunTrust Xxxxxxxx Xxxxxxxx, Inc.		3,540,000		74,342,000		24,000,000		5,194,000
Deutsche Bank Securities Inc.		2,500,000		5,000,000		88,750,000		5,000,000
Credit Suisse Securities (USA) LLC		2,500,000		5,000,000		88,750,000		5,000,000
Greenwich Capital Markets, Inc.		2,505,000		9,508,000		37,471,000		40,000,000
Barclays Capital Inc.		2,505,000		9,508,000		37,741,000		40,000,000
Xxxxxx Xxxxxxx & Co. Incorporated		2,505,000		9,508,000		37,741,000		40,000,000
Citigroup Global Markets Inc.		7,500,000		15,000,000		30,000,000		15,000,000
X.X. Xxxxxx Securities Inc.		7,500,000		15,000,000		30,000,000		15,000,000
Xxxxxxx Lynch, Pierce, Xxxxxx & Xxxxx Incorporated		0		0		0		50,144,000
UBS Securities LLC		7,500,000		15,000,000		30,000,000		15,000,000
BBVA Securities Inc.		1,721,000		3,440,000		6,871,000		3,442,000
BMO Capital Markets Corp.		1,721,000		3,440,000		6,871,000		3,442,000
BNY Mellon Capital Markets, LLC		1,721,000		3,440,000		6,871,000		3,442,000
Comerica Securities, Inc.		1,721,000		3,440,000		6,871,000		3,442,000
DnB NOR Markets, Inc.		1,721,000		3,440,000		6,871,000		3,442,000
Fortis Securities LLC		1,721,000		3,440,000		6,871,000		3,442,000
Lazard Capital Markets LLC		1,721,000		3,440,000		6,871,000		3,442,000
Natixis Bleichroeder Inc.		1,721,000		3,440,000		6,871,000		3,442,000
Xxxxx Xxxxxxx & Co.		1,721,000		3,440,000		6,871,000		3,442,000
Tudor, Pickering, Xxxx & Co. Securities, Inc.		1,721,000		3,440,000		6,871,000		3,442,000
Xxxxx Fargo Securities, LLC		1,721,000		3,440,000		6,871,000		3,442,000
Total	$	250,000,000	$	500,000,000	$	1,000,000,000	$	500,000,000

Schedule 1

SCHEDULE II

ISSUER FREE WRITING PROSPECTUSES

•

Final Term Sheet, dated August 4, 2008, relating to the Notes, as filed pursuant to Rule 433 under the Securities Act and attached as Schedule III hereto.

Schedule II

SCHEDULE III

Filed Pursuant to Rule 433

Registration No. 333-135136

Free Writing Prospectus Dated August 4, 2008

Final Term Sheet

XTO Energy Inc.

$250,000,000 5.000% Senior Notes due 2010

$500,000,000 5.750% Senior Notes due 2013

$1,000,000,000 6.500% Senior Notes due 2018

$500,000,000 6.750% Senior Notes due 2037

The Senior Notes due 2037 offered hereby constitute a further issuance of and will become fungible with the $950,000,000 aggregate principal amount of 6.75% Senior Notes we originally issued on July 19, 2007 and subsequently re-opened on August 24, 2007. The Senior Notes due 2037 will accordingly have the same CUSIP number and will trade interchangeably with the previously issued notes of the series upon settlement.


Trade Date:		August 4, 2008

Settlement Date:		August 7, 2008

Legal Format:		SEC Registered

Expected Ratings
(Xxxxx’x / S&P):		Baa2 / BBB

Security Type:		Senior Notes

Maturity:		August 1, 2010 for the 2010 Notes December 15, 2013 for the 2013 Notes December 15, 2018 for the 2018 Notes August 1, 2037 for the 2037 Notes

Interest Rate:		5.000% per annum in the case of the 2010 Notes 5.750% per annum in the case of the 2013 Notes 6.500% per annum in the case of the 2018 Notes 6.750% per annum in the case of the 2037 Notes

Schedule III-1


Interest Payment Dates:		February 1 and August 1, commencing February 1, 2009 for the 2010 and 2037 Notes
		June 15 and December 15, commencing December 15, 2008 for the 2013 and 2018 Notes

Spread to Benchmark Treasury:		2.48% in the case of the 2010 Notes
		2.53% in the case of the 2013 Notes
		2.58% in the case of the 2018 Notes
		2.63% in the case of the 2037 Notes

Benchmark Treasury and Yield:		2.750% TSY due July 2010: 2.527% in the case of the 2010 Notes
		3.375% TSY due July 2013: 3.237% in the case of the 2013 Notes
		3.875% TSY due May 2018: 3.960% in the case of the 2018 Notes
		5.000% TSY due May 2037: 4.584% in the case of the 2037 Notes

Yield to Maturity:		5.007% in the case of the 2010 Notes
		5.767% in the case of the 2013 Notes
		6.540% in the case of the 2018 Notes
		7.214% in the case of the 2037 Notes

Public Offering Price:		99.988% of the principal amount in the case of the 2010 Notes
		99.931% of the principal amount in the case of the 2013 Notes
		99.713% of the principal amount in the case of the 2018 Notes
		94.391% of the principal amount in the case of the 2037 Notes

Gross Proceeds to Issuer:		$249,970,000 in the case of the 2010 Notes
		$499,655,000 in the case of the 2013 Notes
		$997,130,000 in the case of the 2018 Notes
		$471,955,000 in the case of the 2037 Notes

Net Proceeds to Issuer (Before Expenses):		$249,220,000 in the case of the 2010 Notes
		$496,655,000 in the case of the 2013 Notes
		$990,630,000 in the case of the 2018 Notes
		$467,580,000 in the case of the 2037 Notes

Accrued Interest to Issuer:		$562,500; 6.75% accrued from and including August 1, 2008 to but excluding August 7, 2008 in the case of the 2037 Notes. The accrued interest on the 2037 Notes must be paid by the purchasers of those notes on the settlement date

Total Proceeds to Issuer:		$249,220,000 in the case of the 2010 Notes $496,655,000 in the case of the 2013 Notes $990,630,000 in the case of the 2018 Notes $468,142,500 in the case of the 2037 Notes

Schedule III-2


Optional Redemption:	Redeemable at any time at an amount equal to the principal amount plus a make-whole premium, using a discount rate of Treasury plus 0.375% in the case of the 2010, 2013 and 2018 Notes, and 0.25% in the case of the 2037 Notes

CUSIP:	98385X AR7 in the case of the 2010 Notes
	98385X AS5 in the case of the 2013 Notes
	98385X AT3 in the case of the 2018 Notes
	98385X AM8 in the case of the 2037 Notes

Joint Bookrunning Managers (For all Senior Notes):	Xxxxxx Brothers Inc.
	Banc of America Securities LLC

Joint Bookrunning Managers:
	2010 Notes:	Xxxxxxxxx & Company, Inc.
		Wachovia Capital Markets, LLC
	2013 Notes:	BNP Paribas Securities Corp.
		SunTrust Xxxxxxxx Xxxxxxxx, Inc.
	2018 Notes:	Deutsche Bank Securities Inc.
		Credit Suisse Securities (USA) LLC
	2037 Notes:	Greenwich Capital Markets, Inc.
		Barclays Capital Inc.
		Xxxxxx Xxxxxxx & Co. Incorporated

Co-Managers:	Xxxxxxxxx & Company, Inc.
	Wachovia Capital Markets, LLC
	BNP Paribas Securities Corp.
	SunTrust Xxxxxxxx Xxxxxxxx, Inc.
	Deutsche Bank Securities Inc.
	Credit Suisse Securities (USA) LLC
	Greenwich Capital Markets, Inc.
	Barclays Capital Inc.
	Xxxxxx Xxxxxxx & Co. Incorporated
	Citigroup Global Markets Inc.
	X.X. Xxxxxx Securities Inc.
	Xxxxxxx Lynch, Pierce, Xxxxxx & Xxxxx Incorporated
	UBS Securities LLC
	BBVA Securities, Inc.
	BMO Capital Markets Corp.
	BNY Capital Markets, Inc.
	Comerica Securities, Inc.
	DnB NOR Markets, Inc.
	Fortis Securities LLC
	Lazard Capital Markets LLC
	Natixis Bleichroeder Inc.
	Xxxxx Xxxxxxx & Co.
	Tudor, Pickering, Xxxx & Co. Securities, Inc.
	Xxxxx Fargo Securities, LLC

Schedule III-3

Note: A securities rating is not a recommendation to buy, sell or hold securities and may be subject to revision or withdrawal at any time.

The issuer has filed a registration statement (including a prospectus) with the SEC for the offering to which this communication relates. Before you invest, you should read the prospectus in that registration statement and other documents the issuer has filed with the SEC for more complete information about the issuer and this offering. You may get these documents for free by visiting XXXXX on the SEC Web site at xxx.xxx.xxx. Alternatively, the issuer, any underwriter or any dealer participating in the offering will arrange to send you the prospectus if you request it by calling Xxxxxx Brothers Inc. toll-free at 0-000-000-0000, or Banc of America Securities LLC. at 1-800-294-1322.

Schedule III-4

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XTO ENERGY INC. $250,000,000 5.000% Senior Notes due 2010 $500,000,000 5.750% Senior Notes due 2013 $1,000,000,000 6.500% Senior Notes due 2018 $500,000,000 6.750% Senior Notes due 2037 UNDERWRITING AGREEMENT

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