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                                                                   EXHIBIT 10.15

                                                             [EXECUTION VERSION]


                             SENIOR PROMISSORY NOTE


$24,408,000.00                 New York, New York                 March 31, 1999


         SIERRA WELL SERVICE, INC., a Delaware corporation ("Borrower"), for
value received, hereby promises to pay to the order of Joint Energy Development
Investments II Limited Partnership, a Delaware limited partnership, ("Lender")
the principal amount of TWENTY-FOUR MILLION FOUR HUNDRED AND EIGHT THOUSAND AND
NO/100 DOLLARS ($24,408,000.00) and interest on the unpaid balance of such
principal amount in accordance with Senior Loan Agreement referred to below.

         This Note is a "Senior Note" issued pursuant to the Senior Loan
Agreement dated as of March 31, 1999 (as modified from time to time, the "Senior
Loan Agreement"), between the Borrower, the Senior Lenders named therein, and
Joint Energy Development Investments II Limited Partnership, as Senior Agent.
All capitalized terms used herein shall have the meaning ascribed to such term
in the Senior Loan Agreement unless otherwise defined herein. This Note is
subject to and entitled to the benefits of the Senior Loan Agreement and the
support therefor and the holder of this Note may enforce such rights in
accordance with the Senior Loan Agreement. Without limiting the foregoing, upon
the occurrence of an Event of Default, payments due under this Note may be
accelerated in the manner and with the effect provided in the Senior Loan
Agreement.

         This Note is subject to mandatory and optional repayments, in whole or
in part, as specified in the Senior Loan Agreement. Payments of principal and
interest due on this Note paid in lawful money of the United States of America
to the Senior Agent in accordance with the terms of the Senior Loan Agreement.

         Reference is made to the $30,000,000 Senior Secured Note (Tranche A)
dated as of September 30, 1997 ("Prior Note"), made by the Borrower and payable
to the order of Joint Energy Development Investments Limited Partnership. The
Prior Note was assigned to Joint Energy Development Investments II Limited
Partnership. The indebtedness under the Prior Note continues under the Senior
Notes and the execution of the Senior Notes does not indicate a payment,
satisfaction, novation, or discharge thereof.

         The Lender is hereby authorized to record all Loans and all payments
and prepayments hereunder. The failure of the Lender to record any such amounts
shall not diminish or impair the Borrower's obligation to repay all principal
advanced and to pay all interest accruing under this Note.



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         The Borrower and any and each co-maker, guarantor, accommodation party,
endorser or other Person liable for the payment or collection of this Note
expressly waive demand and presentment for payment, notice of nonpayment, notice
of intent to accelerate, notice of acceleration, protest, notice of protest,
notice of dishonor, bringing of suit, and diligence in taking any action to
collect amounts called for hereunder and in the handling of Collateral at any
time existing as security in connection herewith, and shall be directly and
primarily liable for the payment of all sums owing and to be owing hereon,
regardless of and without any notice, diligence, act or omission as or with
respect to the collection of any amount called for hereunder or in connection
with any Lien at any time had or existing as security for any amount called for
hereunder.

         It is the intention of the Senior Lenders and the Borrower to conform
strictly to any applicable usury laws. Accordingly, the terms of the Senior Loan
Agreement relating to the prevention of usury will be strictly followed.

         THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED AND ENFORCED IN ACCORDANCE
WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO PRINCIPLES OF CHOICE OF
LAWS.



                                                     SIERRA WELL SERVICE, INC.



                                                     By: /s/ Bill E. Coggin
                                                        -----------------------
                                                     Name: Bill E. Coggin
                                                     Title: Vice Chairman



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