Common use of Capitalization of the Partnership Clause in Contracts

Capitalization of the Partnership. As of the date hereof and immediately prior to the issuance of Units by the Partnership, the issued and outstanding limited partner interests of the Partnership consist of 110,694,138 Common Units, 22,640,000 Class A Units and 19,954,389 Class B Units as such terms are defined in the Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same has been and may be amended or restated at or prior to the applicable Closing Date, the “Partnership Agreement”). All outstanding Common Units, Class A Units and Class B Units and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware LP Act and as otherwise described in the Prospectus). MarkWest Hydrocarbon owns 8,900,000 Class A Units and (ii) MarkWest Energy GP owns 13,740,000 Class A Units, in each case free and clear of all liens, encumbrances, security interests, equities, charges or claims (“Liens”), except as may arise under the Amended and Restated Credit Agreement dated as of July 1, 2010, as supplemented by the Joinder Agreement dated July 29, 2010 and the Joinder Agreement dated June 15, 2011 and as amended by the First Amendment thereto dated as of September 7, 2011, the Second Amendment thereto dated as of December 29, 2011 and the Third Amendment thereto dated as of June 29, 2012 (as so supplemented and amended, the “Credit Agreement”) among the Partnership, Xxxxx Fargo Bank, National Association, as administrative agent, RBC Capital Markets Corporation, as syndication agent, and the other parties named therein, or as described in the Pricing Disclosure Package and the Prospectus.

Capitalization of the Partnership. As of the date hereof and immediately prior to the issuance of Units by the Partnership, the issued and outstanding limited partner interests of the Partnership consist of 110,694,138 102,693,615 Common Units, 22,640,000 Class A Units and 19,954,389 Class B Units as such terms are defined in the Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same has been and may be amended or restated at or prior to the applicable Closing Date, the “Partnership Agreement”). All outstanding Common Units, Class A Units and Class B Units and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware LP Act and as otherwise described in the Prospectus). MarkWest Hydrocarbon owns 8,900,000 Class A Units and (ii) MarkWest Energy GP owns 13,740,000 Class A Units, in each case free and clear of all liens, encumbrances, security interests, equities, charges or claims (“Liens”), except as may arise under the Amended and Restated Credit Agreement dated as of July 1, 2010, as supplemented by the Joinder Agreement dated July 29, 2010 and the Joinder Agreement dated June 15, 2011 and as amended by the First Amendment thereto dated as of September 7, 2011, and the Second Amendment thereto dated as of December 29, 2011 and the Third Amendment thereto dated as of June 29, 2012 (as so supplemented and amended, the “Credit Agreement”) among the Partnership, Xxxxx Fargo Bank, National Association, as administrative agent, RBC Capital Markets Corporation, as syndication agent, and the other parties named therein, or as described in the Pricing Disclosure Package and the Prospectus.

Capitalization of the Partnership. As of the date hereof and immediately prior to the issuance of Units by the Partnership, the issued and outstanding limited partner interests of the Partnership consist of 110,694,138 95,908,615 Common Units, Units and 22,640,000 Class A Units and 19,954,389 Class B Units Units, as such terms are defined in the Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same has been and may be amended or restated at or prior to the applicable Closing Date, the “Partnership Agreement”). All outstanding Common Units, Class A Units and Class B A Units and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware LP Act and as otherwise described in the Prospectus). MarkWest Hydrocarbon owns 8,900,000 Class A Units and (ii) MarkWest Energy GP owns 13,740,000 Class A Units, in each case free and clear of all liens, encumbrances, security interests, equities, charges or claims (“Liens”), except as may arise under the Amended and Restated Credit Agreement dated as of July 1, 2010, as supplemented by the Joinder Agreement dated July 29, 2010 and the Joinder Agreement dated June 15, 2011 and as amended by the First Amendment thereto thereto, dated as of September 7, 2011, 2011 and the Second Amendment thereto thereto, dated as of December 29, 2011 and the Third Amendment thereto dated as of June 29, 2012 (as so supplemented and amended, the “Credit Agreement”) among the Partnership, Xxxxx Fargo Bank, National Association, as administrative agent, RBC Capital Markets Corporation, as syndication agent, and the other parties named therein, or as described in the Pricing Disclosure Package and the Prospectus.

Capitalization of the Partnership. As of the date hereof and immediately prior to the issuance of Units by the Partnershiphereof, the issued and outstanding limited partner interests of the Partnership consist of 110,694,138 117,594,365 Common Units, 22,640,000 Class A Units and 19,954,389 Class B Units as such terms are defined in the Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same has been and may be amended or restated at or prior to the applicable Closing Datedate hereof, the “"Partnership Agreement”"). All outstanding Common Units, Class A Units and Class B Units and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware LP Act and as otherwise described in the Prospectus). As of the date hereof, MarkWest Hydrocarbon owns 8,900,000 Class A Units and (ii) MarkWest Energy GP owns 13,740,000 Class A Units, in each case free and clear of all liens, encumbrances, security interests, equities, charges or claims (“"Liens”"), except as may arise under the Amended and Restated Credit Agreement dated as of July 1, 2010, as supplemented by the Joinder Agreement dated July 29, 2010 and the Joinder Agreement dated June 15, 2011 and as amended by the First Amendment thereto dated as of September 7, 2011, the Second Amendment thereto dated as of December 29, 2011 and the Third Amendment thereto dated as of June 29, 2012 (as so supplemented and amended, the “"Credit Agreement”") among the Partnership, Xxxxx Fargo Bank, National Association, as administrative agent, RBC Capital Markets Corporation, as syndication agent, and the other parties named therein, or as described in the Pricing Disclosure Package and the Prospectus.

Capitalization of the Partnership. As of the date hereof and immediately prior to the issuance of Units by the Partnership, the issued and outstanding limited partner interests of the Partnership consist of 110,694,138 79,189,558 Common Units, Units and 22,640,000 Class A Units and 19,954,389 Class B Units Units, as such terms are defined in the Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same has been and may be amended or restated at or prior to the applicable Closing Date, the “Partnership Agreement”). All outstanding Common Units, Class A Units and Class B A Units and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware LP Act and as otherwise described in the Prospectus). MarkWest Hydrocarbon owns 8,900,000 Class A Units and (ii) MarkWest Energy GP owns 13,740,000 Class A Units, in each case free and clear of all liens, encumbrances, security interests, equities, charges or claims (“Liens”), except as may arise under the Amended and Restated Credit Agreement dated as of July 1, 2010, as supplemented by the Joinder Agreement dated July 29, 2010 and the Joinder Agreement dated June 15, 2011 and as amended by the that First Amendment thereto dated as of September 7, 2011, the Second Amendment thereto dated as of December 29, 2011 and the Third Amendment thereto dated as of June 29, 2012 (as so supplemented and amended, the “Credit Agreement”) among the Partnership, Xxxxx Fargo Bank, National Association, as administrative agent, RBC Capital Markets Corporation, as syndication agent, and the other parties named therein, or as described in the Pricing Disclosure Package and the Prospectus.

Capitalization of the Partnership. As of the date hereof and immediately prior to the issuance of Units by the Partnership, the issued and outstanding limited partner interests of the Partnership consist of 110,694,138 84,939,558 Common Units, Units and 22,640,000 Class A Units and 19,954,389 Class B Units Units, as such terms are defined in the Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same has been and may be amended or restated at or prior to the applicable Closing Date, the “Partnership Agreement”). All outstanding Common Units, Class A Units and Class B A Units and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware LP Act and as otherwise described in the Prospectus). MarkWest Hydrocarbon owns 8,900,000 Class A Units and (ii) MarkWest Energy GP owns 13,740,000 Class A Units, in each case free and clear of all liens, encumbrances, security interests, equities, charges or claims (“Liens”), except as may arise under the Amended and Restated Credit Agreement dated as of July 1, 2010, as supplemented by the Joinder Agreement dated July 29, 2010 and the Joinder Agreement dated June 15, 2011 and as amended by the that First Amendment thereto dated as of September 7, 2011, the Second Amendment thereto dated as of December 29, 2011 and the Third Amendment thereto dated as of June 29, 2012 (as so supplemented and amended, the “Credit Agreement”) among the Partnership, Xxxxx Fargo Bank, National Association, as administrative agent, RBC Capital Markets Corporation, as syndication agent, and the other parties named therein, or as described in the Pricing Disclosure Package and the Prospectus.

Capitalization of the Partnership. As of the date hereof and immediately prior to the issuance of Units by the Partnership, the issued and outstanding limited partner interests of the Partnership consist of 110,694,138 117,594,365 Common Units, 22,640,000 Class A Units and 19,954,389 Class B Units as such terms are defined in the Third Amended and Restated Agreement of Limited Partnership of the Partnership (as the same has been and may be amended or restated at or prior to the applicable Closing Date, the “Partnership Agreement”). All outstanding Common Units, Class A Units and Class B Units and the limited partner interests represented thereby have been duly authorized and validly issued in accordance with the Partnership Agreement and are fully paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by Sections 17-607 and 17-804 of the Delaware LP Act and as otherwise described in the Prospectus). MarkWest Hydrocarbon owns 8,900,000 Class A Units and (ii) MarkWest Energy GP owns 13,740,000 Class A Units, in each case free and clear of all liens, encumbrances, security interests, equities, charges or claims (“Liens”), except as may arise under the Amended and Restated Credit Agreement dated as of July 1, 2010, as supplemented by the Joinder Agreement dated July 29, 2010 and the Joinder Agreement dated June 15, 2011 and as amended by the First Amendment thereto dated as of September 7, 2011, the Second Amendment thereto dated as of December 29, 2011 and the Third Amendment thereto dated as of June 29, 2012 (as so supplemented and amended, the “Credit Agreement”) among the Partnership, Xxxxx Fargo Bank, National Association, as administrative agent, RBC Capital Markets Corporation, as syndication agent, and the other parties named therein, or as described in the Pricing Disclosure Package and the Prospectus.