FIRST AMENDMENT TO STOCKHOLDER AGREEMENT

Exhibit 10.15

FIRST AMENDMENT TO

STOCKHOLDER AGREEMENT

This First Amendment (this “Amendment”) to the Stockholder Agreement of REG Newco, Inc. (now known as Renewable Energy Group, Inc.), a Delaware corporation (the “Company”), is made and entered into effective as of June 29, 2010. Capitalized terms used but not otherwise defined in this Amendment shall have the respective meanings assigned to such terms in the Stockholder Agreement (as defined below).

WHEREAS, the Company, NGP Energy Technology Partners L.P., a Delaware limited partnership (“NGP Energy”), Natural Gas Partners, VIII, L.P., a Delaware limited partnership (collectively with NGP Energy, “NGP”) and certain other Stockholders entered into that certain Stockholder Agreement of the Company, dated as of February 26, 2010 (the “Stockholder Agreement”);

WHEREAS, pursuant to Section 2(a)(ii) of the Stockholder Agreement, subject to certain conditions, NGP is entitled to nominate and elect two representatives to the Company’s Board of Directors; and

WHEREAS, it is the desire of the undersigned to amend the Stockholder Agreement to modify the number of directors of the Company to be nominated and elected by NGP, and to provide NGP with an observer right with respect to Board meetings, upon the terms and conditions set forth herein.

NOW, THEREFORE, in consideration of the mutual promises of the parties, the parties agree and acknowledge as follows:

Section 1. Amendments.

(a) The Stockholder Agreement is amended, as of the date hereof, by replacing the existing Section 2(a)(ii) of the Stockholder Agreement with the following provision:

“(ii) the nomination and election to the Board of (A) for so long as NGP holds at least 2,105,263 shares of Series A Preferred Stock (and/or Common Stock issued or issuable upon conversion of such Series A Preferred Stock) (subject to appropriate adjustments in the event of any stock dividend, stock split, combination or other similar recapitalization affecting such shares), one (1) representative designated by NGP, which number may be increased at any time in the sole discretion of NGP to two (2) representatives effective upon the written request of NGP, (B) for so long as Westway holds at least 657,895 shares of Series A Preferred Stock (and/or Common Stock issued or issuable upon conversion of such Series A Preferred Stock) (subject to appropriate adjustments in the event of any stock dividend, stock split, combination or other similar recapitalization affecting such shares), one (1) representative designated by Westway, (C) for so long as Bunge holds at least 526,316 shares of Series A Preferred Stock (and/or Common Stock issued or issuable upon conversion of such Series A Preferred Stock) (subject to appropriate adjustments in the event of any stock dividend, stock split,

combination or other similar recapitalization affecting such shares), one (1) representative designated by Bunge and (D) for so long as the members of the USBG Group collectively hold at least 1,277,167 shares of Series A Preferred Stock (and/or Common Stock issued or issuable upon conversion of such Series A Preferred Stock) (subject to appropriate adjustments in the event of any stock dividend, stock split, combination or other similar recapitalization affecting such shares), one (1) representative designated by the members of the USBG Group holding a majority of the shares of Series A Preferred Stock (and/or Common Stock issued or issuable upon conversion of the shares of such Series A Preferred Stock) held by members of the USBG Group (Westway, Bunge and the USBG Group are collectively referred to herein as the “Strategic Investors”); provided, however, in the event any of NGP, Westway, Bunge or USBG Group has elected to have all of its shares of Series A Preferred Stock redeemed by the Company pursuant to the Series A Certificate of Designation (a “Redeeming Stockholder”), and the Company is not able to redeem all the shares of Series A Preferred Stock held by the Redeeming Stockholder, then the Redeeming Stockholder shall not lose the right to have its representative(s) nominated and elected to the Board pursuant to this Subsection 2(a)(ii) until such redemption is complete.”

(b) The Stockholder Agreement is amended, as of the date hereof, by replacing the existing Section 7(c) of the Stockholder Agreement with the following provision:

“(c) Observer Rights. The Company shall permit up to four (4) non-voting observers to attend each meeting of the Board and of any committees of the Board, consisting of the President of the Company, an observer appointed by West Central, an observer appointed by Energy Technology Partners, L.L.C. and, for so long as only (1) director has been appointed to the Board by NGP as contemplated in Section 2(a)(ii) above, an observer appointed by NGP; provided however that NGP shall not have the right to appoint an observer pursuant to this Section 7 during the period in which NGP has appointed two (2) directors to the Board as contemplated in Section 2(a)(ii) above. Such observers shall receive advance notice of all such meetings and all materials provided to the directors before and during such meetings. The Company may remove or exclude such observers from any meeting of the Board and of any committees of the Board when such observers’ presence would reasonably be expected to compromise attorney-client confidentiality, would be reasonably necessary to protect highly confidential information or for other similar bona fide corporate reasons. The decision of the Board with respect to the privileged or confidential nature of such information shall be final and binding.”

Section 2. Effect. This Amendment constitutes an amendment to the Stockholder Agreement. The terms and provisions of the Stockholder Agreement and all other documents and instruments relating and pertaining to the Stockholder Agreement shall continue in full force and effect, as amended hereby. In the event of any conflict between the provisions of the Stockholder Agreement and the provisions of this Amendment, the provisions of this Amendment shall control.

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Section 3. Counterparts. This Amendment may be executed in any number of counterparts, each of which shall for all purposes be deemed to be an original, and all such counterparts shall together constitute but one and the same instrument.

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IN WITNESS WHEREOF, the parties hereto have executed this Amendment effective as of the day first above written.

FIRST AMENDMENT TO STOCKHOLDER AGREEMENT

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FIRST AMENDMENT TO STOCKHOLDER AGREEMENT

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FIRST AMENDMENT TO STOCKHOLDER AGREEMENT

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FIRST AMENDMENT TO STOCKHOLDER AGREEMENT

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FIRST AMENDMENT TO STOCKHOLDER AGREEMENT

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FIRST AMENDMENT TO STOCKHOLDER AGREEMENT

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