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                                                                    EXHIBIT 2.2 


                               FIRST AMENDMENT TO
                            ASSET PURCHASE AGREEMENT


         This FIRST AMENDMENT (this "Amendment") to the Asset Purchase
Agreement dated March 5, 1997 (the "Agreement"), by and among UTI Energy Corp.,
a Delaware corporation ("Buyer"), Triad Drilling Corporation, a Delaware
corporation and wholly owned subsidiary of Buyer ("Triad"), and Southland
Drilling Company, Ltd., a Texas limited partnership ("Seller");

                                  WITNESSETH:

         WHEREAS, Buyer and Seller entered into the Agreement whereby Buyer
agreed to buy, and Seller agreed to sell, the Purchased Assets in exchange for
the payment by Buyer of the Purchase Price and the assumption by Buyer of the
Assumed Liabilities; and

         WHEREAS, as permitted by the Agreement, Buyer desires to assign to
Triad Buyer's right to take title to the Purchased Assets;

         NOW, THEREFORE, in consideration of the premises and the mutual terms
and covenants herein contained, and intending to be legally bound hereby, the
parties hereto hereby agree as follows:

         1.      Triad hereby agrees that it shall be bound by and liable for
the obligations of Buyer set forth in Article II of the Agreement.

         2.      The parties hereto agree that (i) the delivery of the
Purchased Assets described in Section 2.6 of the Agreement shall be made to
Triad instead of Buyer, (ii) Seller shall deliver the documents identified in
Section 4.2 of the Agreement to Triad instead of Buyer, and (iii) Triad shall
deliver the General Assignment referred to in Section 4.3(b).

         3.      Due to certain changes involving drill pipe, the Cash Purchase
Price shall be reduced by $182,000.

         4.      Except as expressly amended by this Amendment, the Agreement
remains in full force and effect.

         5.      Capitalized terms used and not otherwise defined herein have
the meanings given such terms in the Agreement.

                    (Signatures Begin on the Following Page)
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         IN WITNESS WHEREOF, the parties have caused this Agreement to be
executed by their respective officers hereunto duly authorized as of the date
first above written.

                                  UTI ENERGY CORP.
                                  
                                  
                                  
                                  By:    /s/ Vaughn Drum                       
                                       ----------------------------------------
                                                Vaughn Drum, President         
                                                                               
                                                                               
                                                                               
                                  SOUTHLAND DRILLING COMPANY, LTD.             
                                                                               
                                                                               
                                                                               
                                  By:    /s/ Neil Hanson                        
                                       ----------------------------------------
                                                                               
                                                                               
                                                                               
                                  TRIAD DRILLING CORPORATION                   
                                                                               
                                                                               
                                                                               
                                  By:    /s/ Vaughn Drum                       
                                       ----------------------------------------
                                                Vaughn Drum, Chairman of       
                                                  the Board and Chief          
                                                   Executive Officer           





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