Exhibit 5.1

April 30, 2010

Cameron International Corporation

1333 West Loop South, Suite 1700

Houston, TX 77027

Gentlemen:

    I am the General Counsel for Cameron International Corporation, a Delaware corporation (the “Company”), and have acted in such capacity in connection with the proposed filing with the Securities and Exchange Commission expected to be made on or about April 30, 2010, under the Securities Act of 1933, as amended, of a Registration Statement on Form S-8 (the “Registration Statement”) for the purpose of registering 8,770,250 shares of common stock, $0.01 par value per share (the “Shares”); said Shares are issuable under the Cameron International Corporation 2005 Equity Incentive Plan (the “Plan”).  In such capacity, I have examined the Restated Certificate of Incorporation and the Third Amended and Restated By-Laws of the Company, the Plans, and such other documents of the Company as I have deemed necessary or appropriate for the purposes of the opinion expressed herein.

Based upon the foregoing, I advise you that, in my opinion, when issued in accordance with the provisions of the Plan, the Shares have been duly authorized and, when issued in accordance with the terms of the Plan and related agreements thereunder, will be validly issued, fully paid and non-assessable.

The opinion expressed above is limited to the Delaware General Corporation Law and the federal laws of the United States of America. I am not admitted to the practice of law in the State of Delaware.

I hereby consent to the filing of this opinion as an exhibit to the Registration Statement. In giving this consent, I do not thereby admit that I come into the category of persons whose consent is required under Section 7 of the Securities Act of 1933 or the rules and regulations of the Securities and Exchange Commission promulgated thereunder.

Very truly yours,

/s/  William C. Lemmer                                  

William C. Lemmer

Senior Vice President & General Counsel