[Cooper Cameron Corporation Letterhead]

                                                                    Exhibit 5.1

                                 April 21, 2003

Cooper Cameron Corporation
1333 West Loop South, Suite 1700
Houston, TX 77027

Gentlemen:

     I am the General Counsel for Cooper Cameron Corporation, a Delaware
corporation (the "Company"), and have acted in such capacity in connection with
the registration under the Securities Act of 1933, as amended, of 1,000,000
shares (the "Shares") of the Company's common stock, $.01 par value (the "Common
Stock"), to be offered upon the terms and subject to the conditions set forth in
the Company's Registration Statement on Form S-8 (the "Registration Statement")
relating thereto to be filed with the Securities and Exchange Commission.

     In connection therewith, I have examined originals or copies certified or
otherwise identified to my satisfaction of the Amended and Restated Certificate
of Incorporation of the Company, the Second Amended and Restated By-laws of the
Company, the corporate proceedings with respect to the Shares and the offering
thereof, certificates of public officials, statutes and such other documents and
instruments as I have deemed necessary or appropriate for the expression of the
opinions contained herein.

     I have assumed the authenticity and completeness of all records,
certificates and other instruments submitted to me as originals, the conformity
to original documents of all records, certificates and other instruments
submitted to me as copies, the authenticity and completeness of the originals of
those records, certificates and other instruments submitted to me as copies and
the correctness of all statements of fact contained in all records, certificates
and other instruments that I have examined.

     Based upon the foregoing, and having a regard for such legal considerations
as I have deemed relevant, I am of the opinion that:

          (i) The Company has been duly incorporated and is validly existing in
     good standing under the laws of the State of Delaware.

          (ii) The Shares proposed to be sold by the Company have been duly and
     validly authorized for issuance and, when issued in accordance with the
     terms of the Registration Statement, and subject to compliance with any
     applicable Blue Sky laws, will be validly issued, fully paid and
     non-assessable.

     I hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement.

                              Very truly yours,

                              /s/ William C. Lemmer
                              --------------------------------------------
                              William C. Lemmer
                              Vice President, General Counsel
                              and Secretary