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                                                                     EXHIBIT 5.1

                                 August 17, 2001

Patterson-UTI Energy, Inc.
4510 Lamesa Highway
P.O. Box 1416
Snyder, Texas 79550

Re: Adoption of the 2001 Long-Term Incentive Plan of Patterson-UTI Energy, Inc.

Gentlemen:

         We have acted as counsel to Patterson-UTI Energy, Inc., a Delaware
corporation ("Company"), in connection with the registration under the
Securities Act of 1933 ("Securities Act") on Form S-8 (the "Registration
Statement") of 2,000,000 shares of the Company's common stock, par value $.01
per share ("Common Stock"), covered by the 2001 Long-Term Incentive Plan of
Patterson-UTI Energy, Inc. (the "Plan").

         In connection with the foregoing, we have examined: (a) the Restated
Certificate of Incorporation and the Bylaws of the Company, (b) the Plan, (c)
the Minutes of the Board of Directors of the Company, (d) the applicable laws of
the State of Delaware, and (e) a copy of the Registration Statement and the
exhibits and supplements to each.

         Based on such examination, and having regard for such legal
considerations as we deem relevant, we are of the opinion that the Company is
authorized to issue and to sell the Common Stock; and the Common Stock, when
issued, delivered and paid for in accordance with the terms and conditions of
the Plan, will be legally issued, fully paid and nonassessable.

         We hereby consent (i) to be named in the Registration Statement, and in
the Prospectus that constitutes a part thereof, as attorneys passing upon the
validity of the issuance of the Common Stock on behalf of the Company, and (ii)
to the filing of this Registration Statement.

         This opinion is to be used solely for the purpose of the registration
of the Common Stock and may not be used for any other purpose.

                                           Very truly yours,

                                           /s/ BAKER & HOSTETLER LLP