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                                                                     EXHIBIT 5.1


                   [LETTERHEAD OF FULBRIGHT & JAWORSKI L.L.P.]


December 29, 2000


UTI Energy Corp.
16800 Greenspoint Park Drive
Suite 225N
Houston, Texas 77060

Gentlemen:

         We have acted as counsel for UTI Energy Corp., a Delaware corporation
(the "Company"), in connection with the registration under the Securities Act of
1933 of 800,000 shares of the Company's common stock, $.001 par value (the
"Shares"), to be offered upon the terms and subject to the conditions set forth
in the Company's Amended and Restated 1997 Long-Term Incentive Plan (the "1997
Plan").

         In connection therewith, we have examined originals or copies,
certified or otherwise identified to our satisfaction, of the Restated
Certificate of Incorporation of the Company, as amended, the amended Bylaws of
the Company, the 1997 Plan, the records of relevant corporate proceedings with
respect to the offering of the Shares and such other documents and instruments
as we have deemed necessary or appropriate for the expression of the opinions
contained herein. We also have examined the Company's Registration Statement on
Form S-8 (the "Registration Statement") to be filed with the Securities and
Exchange Commission with respect to the Shares.

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

         Based on the foregoing, and having regard for such legal considerations
as we have deemed relevant, we are of the opinion that the Shares have been duly
and validly authorized for issuance and, when issued in accordance with the
terms of the 1997 Plan, will be duly and validly issued, fully paid and
nonassessable.

         The opinions expressed herein relate solely to, are based solely upon
and are limited exclusively to the laws of the State of Delaware and the federal
laws of the United States of America, to the extent applicable.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.

                                       Very truly yours,

                                       /s/ Fulbright & Jaworski L.L.P.

                                       Fulbright & Jaworski L.L.P.