Lock-Up Agreement

Exhibit 99.4

Lock-Up Agreement

July 28, 2006

UBS Securities LLC
Xxxxx Xxxxxxx & Co., Inc.
   as Managing Underwriters (“Managing Underwriters”)
c/o UBS Securities LLC
000 Xxxx Xxxxxx
Xxx Xxxx, Xxx Xxxx 00000-0000

Ladies and Gentlemen:

          This Lock-Up Agreement is being delivered to you in connection with the proposed Underwriting Agreement (the “Underwriting Agreement”) to be entered into by US BioEnergy Corporation, a South Dakota corporation (the “Company”), and you and the other underwriters named in Schedule A to the Underwriting Agreement, with respect to the public offering (the “Offering”) of common stock, $0.01 par value, of the Company (the “Common Stock”).

          In order to induce you to enter into the Underwriting Agreement, the undersigned agrees that, for a period (the “Lock-Up Period”) beginning on the date hereof and ending on, and including, the date that is 180 days after the date of the final prospectus relating to the Offering, the undersigned will not, without the prior written consent of the Managing Underwriters, (i) sell, offer to sell, contract or agree to sell, hypothecate, pledge, grant any option to purchase or otherwise dispose of or agree to dispose of, directly or indirectly, or file (or participate in the filing of) a registration statement with the Securities and Exchange Commission (the “Commission”) in respect of, or establish or increase a put equivalent position or liquidate or decrease a call equivalent position within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, and the rules and regulations of the Commission promulgated thereunder with respect to, any Common Stock or securities convertible into or exchangeable or exercisable for Common Stock, or warrants or other rights to purchase Common Stock or any such securities, (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of Common Stock or any securities convertible into or exchangeable or exercisable for Common Stock, or warrants or other rights to purchase Common Stock or any such securities, whether any such transaction is to be settled by delivery of Common Stock or such other securities, in cash or otherwise, or (iii) publicly announce an intention to effect any transaction specified in clause (i) or (ii) above. The foregoing sentence shall not apply to (a) the registration of the offer and sale of Common Stock as contemplated by the Underwriting Agreement and the sale of the Common Stock to the Underwriters (as defined in the Underwriting Agreement) in the Offering, (b) bona fide gifts, provided that the recipient thereof agrees in writing with the Managing Underwriters to be bound by the terms of this Lock-Up Agreement, (c) transfers to any trust, partnership or limited liability company for the direct or indirect benefit of the undersigned and/or the

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immediate family of the undersigned, provided that such transferee agrees in writing with the Managing Underwriters to be bound by the terms of this Lock-Up Agreement, (d) if the undersigned is a corporation, limited liability company or partnership, transfers to a wholly-owned subsidiary of the undersigned or to the direct or indirect stockholders, members or partners or other affiliates of the undersigned, provided that no filing pursuant to Section 16 of the Securities Exchange Act of 1934, as amended, is required as result of such transfer and such transferee agrees in writing with the Managing Underwriters to be bound by the terms of this Lock-Up Agreement and (e) transfers which occur by operation of law, such as the rules of intestate succession, provided that such transferee agrees in writing with the Managing Underwriters to be bound by the terms of this Lock-Up Agreement. For purposes of this paragraph, “immediate family” shall mean the undersigned and the spouse, any lineal descendent, father, mother, brother, sister, father-in-law, mother-in-law, brother-in-law or sister-in-law of the undersigned.

          In addition, the undersigned hereby waives any rights the undersigned may have to require registration of Common Stock in connection with the filing of a registration statement relating to the Offering. The undersigned further agrees that, for the Lock-Up Period, the undersigned will not, without the prior written consent of the Managing Underwriters, make any demand for, or exercise any right with respect to, the registration of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, or warrants or other rights to purchase Common Stock or any such securities.

          Notwithstanding the above, if (a) during the period that begins on the date that is fifteen (15) calendar days plus three (3) business days before the last day of the Lock-Up Period and ends on the last day of the Lock-Up Period, the Company issues an earnings release or material news or a material event relating to the Company occurs; or (b) prior to the expiration of the Lock-Up Period, the Company announces that it will release earnings results during the sixteen (16) day period beginning on the last day of the Lock-Up Period, then the restrictions imposed by this Lock-Up Agreement shall continue to apply until the expiration of the date that is fifteen (15) calendar days plus three (3) business days after the date on which the issuance of the earnings release or the material news or material event occurs.

          In addition, the undersigned hereby waives any and all preemptive rights, participation rights, resale rights, rights of first refusal and similar rights that the undersigned may have in connection with the Offering or with any issuance or sale by the Company of any equity or other securities before the Offering, except for any such rights as have been heretofore duly exercised.

          The undersigned hereby confirms that the undersigned has not, directly or indirectly, taken, and hereby covenants that the undersigned will not, directly or indirectly, take, any action designed, or which has constituted or will constitute or might reasonably be expected to cause or result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of shares of Common Stock.

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          If (i) the Company notifies you in writing that it does not intend to proceed with the Offering, (ii) the registration statement filed with the Commission with respect to the Offering is withdrawn or (iii) for any reason the Underwriting Agreement shall be terminated prior to the “time of purchase” (as defined in the Underwriting Agreement), this Lock-Up Agreement shall be terminated and the undersigned shall be released from its obligations hereunder.

Yours very truly,

Name:

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