Exhibit 5.1

425 MARKET STREET SAN FRANCISCO CALIFORNIA 94105-2482 TELEPHONE: 415.268.7000 FACSIMILE: 415.268.7522 WWW.MOFO.COM MORRISON & FOERSTER LLP NEW YORK, SAN FRANCISCO, LOS ANGELES, PALO ALTO, SAN DIEGO, WASHINGTON, D.C. DENVER, NORTHERN VIRGINIA, SACRAMENTO, WALNUT CREEK TOKYO, LONDON, BEIJING, SHANGHAI, HONG KONG, SINGAPORE, BRUSSELS

November 11, 2010

Clean Energy Fuels Corp.

3020 Old Ranch Parkway, Suite 400

Seal Beach, CA 90740

Re:3,450,000 Shares of Common Stock of Clean Energy Fuels Corp.

Ladies and Gentlemen:

We have acted as counsel to Clean Energy Fuels Corp., a Delaware Corporation (the “Company”), in connection with the sale by the Company of up to 3,450,000 shares of the Company’s Common Stock, par value $0.0001 per share, including 450,000 shares that may be sold upon the exercise of an over-allotment option (collectively, the “Shares”), pursuant to a Registration Statement on Form S-3 (File No. 333-168433) originally filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”) on July 30, 2010 (the “Registration Statement”) and the related prospectus included therein (the “Prospectus”) and the prospectus supplement to be filed with the Commission pursuant to Rule 424(b) promulgated under the Act (the “Prospectus Supplement”).  All of the Shares are to be sold by the Company as described in the Registration Statement and the related Prospectus and Prospectus Supplement.

In connection with this opinion, we have examined the Company’s Restated Certificate of Incorporation, and the Company’s By-laws, both as currently in effect, such other records of the corporate proceedings of the Company and certificates of the Company’s officers as we have deemed relevant, the Registration Statement and the exhibits thereto, and the related Prospectus and Prospectus Supplement.  In addition, we have examined such records, documents, certificates of public officials and the Company, made such inquiries of officials of the Company and considered such questions of law as we have deemed necessary for the purpose of rendering the opinion set forth herein.  In such examination, we have assumed the genuineness of all signatures and the authenticity of all items submitted to us as originals and the conformity with originals of all items submitted to us as copies.

Based upon, subject to and limited by the foregoing, we are of the opinion that the Shares have been duly and validly authorized and upon issuance, delivery and payment therefor in the manner contemplated by the Registration Statement, the Prospectus and the Prospectus Supplement, will be legally issued, fully paid and nonassessable.

We express no opinion as to matters governed by any laws other than the Delaware General Corporation Law in effect on the date hereof.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement and to reference to us under the caption “Legal Matters” in the Prospectus Supplement.  In giving such consent, we do not hereby admit that we are acting within the category of persons whose consent is required under Section 7 of the Act or the rules or regulations of the Commission thereunder.

Very truly yours,

/s/ Morrison & Foerster LLP