1
                                                                     EXHIBIT 5.1


                                [P&H LETTERHEAD]



                                October 30, 2000



U.S. Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549

         Re:      Registration Statement on Form S-8
                  Marine Drilling Companies 401(k) Profit Sharing Plan

Ladies and Gentlemen:

         We have acted as counsel to Marine Drilling Companies, Inc., a Texas
corporation (the "Company"), in connection with the preparation of a
registration statement on Form S-8 (the "Registration Statement") registering up
to 100,000 shares of common stock, par value $.01 per share (the "Common
Stock"), of the Company for issuance pursuant to the Marine Drilling Companies
401(k) Profit Sharing Plan (the "Plan").

         We have examined the Plan and such corporate records, documents,
instruments and certificates of the Company, and have reviewed such questions of
law as we have deemed necessary, relevant or appropriate to enable us to render
the opinion expressed herein. In such examination, we have assumed without
independent investigation the authenticity of all documents submitted to us as
originals, the genuineness of all signatures, the legal capacity of all natural
persons, and the conformity of any documents submitted to us as copies to their
respective originals. As to certain questions of fact material to this opinion,
we have relied without independent investigation upon statements or certificates
of public officers of the Company.

         Based upon such examination and review, we are of the opinion that:

         1. The shares of Common Stock to be issued under the Plan are duly
authorized.

         2. When the Common Stock is issued and delivered in accordance with and
pursuant to the terms of the Plan, such Common Stock will be validly issued,
fully paid and nonassessable.