EXHIBIT A


         Each of the undersigned hereby agrees that this Amendment No. 4 dated
June 26, 2002, to Schedule 13D filed November 2, 2000, to which this Agreement
is attached as Exhibit A, and any amendments thereto, may be filed on behalf of
each such person.

         This Agreement may be executed in any number of counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.


Dated: July 2, 2002


                                   WEATHERFORD INTERNATIONAL LTD.

                                   By: /s/ BURT M. MARTIN
                                      ------------------------------------------
                                   Name:  Burt M. Martin
                                   Title: Senior Vice President, General Counsel
                                          and Secretary

                                   WEATHERFORD INTERNATIONAL, INC.

                                   By: /s/ BURT M. MARTIN
                                      ------------------------------------------
                                   Name:  Burt M. Martin
                                   Title: Senior Vice President, General Counsel
                                          and Secretary

                                   WEUS HOLDING, INC.

                                   By:  /s/ BURT M. MARTIN
                                      ------------------------------------------
                                   Name:  Burt M. Martin
                                   Title: Assistant Secretary



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