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                                                                    EXHIBIT 10.8

                       MIDLAND OPTION EXERCISE AGREEMENT

                 NOTE:  SIGNATURE MUST BE PROVIDED BELOW AND ON
                           THE SCHEDULE OF OWNERSHIP.

              PLEASE READ THE ACCOMPANYING INSTRUCTIONS CAREFULLY.


To Midland Resources, Inc., a Texas corporation (the "Company"):

         The undersigned acknowledges that the attached Schedule of Ownership
("Ownership Schedule") is a true and complete list of all of the issued and
outstanding options, other than Midland Exchange Stock Options (as such term is
defined in the Agreement and Plan of Merger described below) to acquire shares
of the common stock, par value $.001 per share, of the Company ("Options")
granted to the undersigned pursuant to the Company's 1997 Board of Directors'
Stock Incentive Plan, the 1995 Directors' Stock Option Plan, the 1996 Long-Term
Incentive Plan or the 1994 Long-Term Incentive Plan (collectively, the "Midland
Stock Plans") and that, except for Midland Exchange Options, if any, and as set
forth herein, the undersigned does not have the right to acquire any stock in
the Company or any options, warrants or other rights to acquire shares of
capital stock of or equity interests in the Company, or similar securities or
contractual obligations the value of which is derived from the value of an
equity interest in the Company, or securities convertible into or exchangeable
for capital stock of or equity interests in, or similar securities or
contractual obligations of, the Company.

         The undersigned acknowledges that pursuant to Section 2.7(b)(iii) of
the Agreement and Plan of Merger among Vista Resources Partners, L.P.
("Vista"), the Company, Vista Energy Resources, Inc. ("Newco") and Midland
Merger Co.  ("Merger Sub"), dated as of May 22, 1998, effective as of the
consummation of the merger among Vista, the Company, Newco and Merger Sub (the
"Effective Time"), each Option (other than Midland Exchange Stock Options)
shall be assumed by Newco in the manner described in such section.

         The parties hereto agree that, effective as of the Effective Time, a
"change of control" shall have occurred, upon which event all of the
undersigned's Options that are still outstanding and not yet exercisable or are
subject to restrictions shall become immediately exercisable and all
restrictions shall be removed as of the Effective Time.

         Effective as of the Effective Time, the parties hereto agree that, if
at any time after the Effective Time the undersigned is no longer employed by
or engaged as a consultant for Newco or any subsidiary thereof, then the
undersigned shall be eligible to exercise such Options for a period of 120 days
after the date of such termination of employment or engagement; provided,
however,
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that upon expiration of such 120-day period, all of the undersigned's Options
that remain unexercised shall be automatically cancelled without any further
action on the part of any party.

         This Agreement shall serve as an amendment to the terms and provisions
of the Undersigned's Options to the extent that the terms and provisions of
such Options are inconsistent with the terms and provisions of this Agreement.

                                            MIDLAND RESOURCES, INC.

                                            By:                               
                                                ------------------------------
                                            Name:                             
                                                  ----------------------------
                                            Title:                            
                                                   ---------------------------


                                            OPTION HOLDER

                                            By:                               
                                                ------------------------------
                                            Name:                             
                                                  ----------------------------
                                            Title:                            
                                                   ---------------------------


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                             SCHEDULE OF OWNERSHIP