Exhibit 10.A

STOCK PURCHASE AGREEMENT

     This Stock Purchase Agreement (the “Agreement”) is made and entered into
this 18th day of July, 2005, among the parties identified on Exhibit “A”
(collectively, the “Sellers” and individually a “Seller”), El Paso Production
Holding Company, a Delaware corporation (the “Purchaser”), and Medicine Bow
Energy Corporation, a Delaware corporation (the “Company”).

RECITALS

     A. WHEREAS, Sellers are the owners of 100% of the equity securities,
warrants and any other stock rights of the Company outstanding on the date set
forth above prior to the Closing, including Class A Common Stock (including,
without limitation, all shares of Class A Common Stock issuable upon conversion
of the Series “A” Redeemable Convertible Preferred Stock), Series “A” Redeemable
Convertible Preferred Stock, Class A-12.5 Common Stock, Class A-25 Common Stock
and the Class A Common Stock Warrant (collectively, the “Shares”) in the amounts
set forth next to each Seller’s name on Exhibit “B”; and

     B. WHEREAS, Purchaser desires to purchase all (100%) of Sellers’ Shares and
Sellers desire to sell such Shares for the Aggregate Purchase Price in
accordance with the terms and conditions of this Agreement.

AGREEMENT

     NOW, THEREFORE, in consideration of the foregoing recitals, the agreements
contained herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Parties agree as follows:

     1. Agreement of Sale and Purchase of Shares. Subject to the terms and
conditions contained in this Agreement, Sellers shall sell to Purchaser and
Purchaser shall purchase from Sellers all of the Shares identified on Exhibit
“B”.

     2. Purchase Price; Closing.

     a. Purchase Price. Subject to the terms and conditions contained in this
Agreement, on the Closing Date, the Purchaser shall pay to the Sellers, in the
aggregate, an amount equal to $814,200,000.00, subject to adjustment as provided
in the next succeeding sentence and Section 3 (the “Aggregate Purchase Price”),
in consideration for the Shares. The Aggregate Purchase Price shall be reduced
on a dollar-for-dollar basis by (1) the total amount (the “Bonus Plan Payout
Amount”) payable in cash to participants in the “bonus pool” portion of the
Company’s 2004 Equity Incentive Plan (the “Bonus Pool”) in connection with the
consummation of the transactions contemplated by this Agreement (which, for the
avoidance of doubt, does not include any amounts payable in respect of the
Shares (including, without limitation, those issued pursuant to the Company’s
2004 Equity Incentive Plan) pursuant to the immediately preceding sentence),
which amount will be (A) provided in writing by the Company to

 

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the Purchaser not less than two business days prior to the Closing Date and
(B) paid by the Purchaser on the Closing Date pursuant to Section 11(b)(II) and
(2) the Accrued Tax Amount. The Aggregate Purchase Price (as adjusted pursuant
to this Section 2(a) and Section 3), less the Bonus Plan Payout Amount and the
Accrued Tax Amount, is herein referred to as the “Share Purchase Price.”

     b. Closing. The closing of this transaction shall be held at 9:00 a.m. on
Wednesday, August 31, 2005, or, if the conditions set forth in Section 10 have
not been satisfied by that date, two business days after the date on which the
last of the conditions set forth in Section 10 shall have been satisfied or
waived, in the offices of the Company at 1225 Seventeenth Street, Suite 1900,
Denver, Colorado 80202, or at such other time, place or method to be mutually
agreed upon by the Parties (hereinafter, the “Closing” or “Closing Date”).

     c. Withholding Rights. The Purchaser (in consummating the transactions
contemplated by this Agreement) and the Company (from and after the Closing
Date) shall be entitled to deduct and withhold from the consideration otherwise
payable pursuant to this Agreement to any officer or employee of the Company (or
any investment vehicle controlled by such officer or employee or formed by such
officer or employee for estate planning purposes) such amounts as the Purchaser
or the Company may be required to deduct and withhold with respect to the making
of such payment under any provision of federal, state, local or foreign tax law.
If the Purchaser or the Company so withholds amounts, such amounts shall be
remitted to the appropriate tax authority and treated for all purposes of this
Agreement as having been paid to the Person in respect of whom the Purchaser or
the Company made such deduction or withholding.

     3. Title Defects and Environmental Defects.

     a. Title Defects. As soon as reasonably practicable (and on an ongoing
basis), but no later than 5:00 p.m. MDT on Wednesday, August 24, 2005 (the
“Objection Deadline”), the Purchaser may notify the Sellers in writing of Title
Defects affecting assets of the Company, its Subsidiaries or Four Star. The
Purchaser’s notice asserting Title Defects shall include a reasonably detailed
description and explanation (including any available supporting documentation)
of each Title Defect claimed, the assets affected, and the value that the
Purchaser in good faith attributes to the Title Defect, which shall not exceed
the Allocated Value of such property. The Purchaser and the Sellers shall meet
periodically to attempt to agree on resolution with respect to Title Defects.
The Sellers shall have the right, but not the obligation, to attempt, at their
sole cost, to cure or remove any Title Defects. The Sellers’ election to attempt
to cure a Title Defect shall not constitute a waiver of Sellers’ right to
dispute the existence, nature or value of, or cost to cure, the Title Defect. In
the event that any Title Defect(s) as to which the Purchaser has given the
Sellers timely notice as provided in this Section 3(a) are not remedied or cured
prior to Closing, then, subject to the other provisions of this Section 3, the
Aggregate Purchase Price shall be reduced by the aggregate value of all such
uncured Title Defects, determined as follows: (1) where the Sellers agree in
writing with the value of the Title Defect as set forth in the Purchaser’s
notice, that value shall be the value of the Title Defect; (2) if the Title
Defect is a lien, encumbrance or other charge

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upon a property which is undisputed and liquidated in amount, then the value of
the Title Defect shall be the lesser of (A) the Allocated Value of such property
or (B) the amount necessary to be paid to the obligee to remove the Title Defect
from the interest of the Company, its Subsidiaries or, in the case of Four Star,
the percentage equity interest of MBOW Four Star Corporation in Four Star
multipled by Four Star’s interest, as applicable, in the affected property;
(3) if the Allocated Value for a property is positive and the Title Defect
represents a discrepancy between the Net Revenue Interest for such property and
the Net Revenue Interest for that property stated on Exhibit “C”, then the value
of such Title Defect shall be the product of the Allocated Value for such
property multiplied by a fraction, the numerator of which is the decrease in Net
Revenue Interest and the denominator of which is the Net Revenue Interest stated
on Exhibit “C” (it being understood that if such reduction in Net Revenue
Interest is not accompanied by a proportionate decrease in the Working Interest
then such descrepency shall constitute a separate Title Defect); and (4) if the
Title Defect represents an obligation, encumbrance, burden or charge upon or
other defect in title to the affected property of a type not described in
subsections (1), (2) or (3) above, the value of the Title Defect shall be
determined by taking into account the Allocated Value for the property so
affected, the portion of the property affected by the Title Defect, the legal
effect of the Title Defect, the potential economic effect of the Title Defect
over the life of the affected property, and such other factors as are
appropriate to make a proper evaluation, in each case net to the interest, as
represented on Exhibit “C”, of the Company, its Subsidiaries or, in the case of
Four Star, the percentage equity interest of MBOW Four Star Corporation in Four
Star multipled by Four Star’s interest, as applicable, in the affected property.

     b. Environmental Defects. As soon as reasonably practicable (and on an
ongoing basis), but no later than the Objection Deadline, the Purchaser may
notify the Sellers in writing of any Environmental Defects. The Purchaser’s
notice asserting Environmental Defects must include a reasonably detailed
description and explanation (including any available supporting documentation)
of each Environmental Defect claimed, the properties affected, and the value
(net to the interest of the Company, its Subsidiaries or, in the case of Four
Star, MBOW Four Star Corporation’s percentage equity interest in Four Star
multiplied by Four Star’s interest, as applicable, in the affected property)
that the Purchaser in good faith attributes to the Environmental Defect. The
Purchaser and the Sellers shall meet periodically to attempt to agree on
resolution with respect to Environmental Defects. The Sellers shall have the
right, but not the obligation, to attempt, at their sole cost, to cure or remove
any alleged Environmental Defects. Sellers’ election to attempt to cure an
Environmental Defect shall not constitute a waiver of Sellers’ right to dispute
the existence, nature, or value of, or cost to cure, the Environmental Defect.
In the event that any Environmental Defect(s) as to which the Purchaser has
given the Sellers timely notice as provided in this Section 3(b) are not
remedied or cured prior to Closing, then, subject to the other provisions of
this Section 3, the Aggregate Purchase Price shall be reduced by the aggregate
value of all such uncured Environmental Defects, taking into account the
following (in each case, net to the interest of the Company, its Subsidiaries
or, in the case of Four Star, the percentage equity interest of MBOW Four Star
Corporation in Four Star multipled by Four Star’s interest, as applicable in the
affected property): (1) the legal effect of the Environmental Defects,
including, but not limited to, potential fines and penalties which may be
incurred until

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such time as the Environmental Defects are remedied; (2) the potential economic
effect of the Environmental Defects and the potential remedy over the life of
the affected assets; (3) the estimated costs and expenses to correct such
Environmental Defects in the most cost effective manner reasonably available,
consistent with Environmental Laws, taking into account that non-permanent
remedies (such as mechanisms to contain or stabilize hazardous materials
including monitoring site conditions, natural attenuation, risk-based corrective
action, institutional controls or other appropriate restrictions on the use of
property, caps, dikes, encapsulation, leachate collection systems, etc.) may be
the most cost effective manner reasonably available; and (4) such other factors
as are necessary to make a proper evaluation.

     c. Title Benefits. Should Sellers discover any Title Benefit prior to
Closing, Sellers shall (as soon as practicable but in any case at least two
business days prior to the Closing Date) deliver to the Purchaser a notice that
includes (1) a specific description of the Title Benefit and the properties
affected and (2) the Sellers’ good faith estimate of the amount by which the
value of the interest of the Company, its Subsidiaries or, in the case of Four
Star, the percentage equity interest of MBOW Four Star Corporation in Four Star
multipled by Four Star’s interest, as applicable, in the affected property has
been increased as a result of such Title Benefit. The value of all timely
asserted Title Benefits shall be offset against the value of the Title Defects
and Environmental Defects, but in no event shall the Aggregate Purchase Price be
increased due to any Title Benefit. The aggregate value (determined in
accordance with Section 3(a) and Section 3(b)) of all timely asserted Title
Defects and Environmental Defects (excluding De Minimis Defects) that remain
uncured at Closing, net of the value of all Title Benefits timely asserted by
the Sellers, is referred to herein as the “Net Defect Amount.” If the value of
all timely asserted Title Benefits exceeds the value of all timely asserted
Title Defects and Environmental Defects, then the Net Defect Amount shall be
zero.

     d. Defect Threshold and Defect Deductible. Notwithstanding anything
contained in this Agreement to the contrary, the Purchaser shall not be entitled
to an Aggregate Purchase Price reduction for any individual Title Defect or
Environmental Defect that has a value (determined in accordance with
Section 3(a) or Section 3(b)) of less than $25,000 (a “De Minimis Defect”). In
addition, notwithstanding anything contained in this Agreement to the contrary,
the Purchaser shall not be entitled to an Aggregate Purchase Price reduction for
Title Defects pursuant to Section 3(a) or for Environmental Defects pursuant to
Section 3(b) unless the Net Defect Amount exceeds $20,000,000 (the “Defect
Threshold”). If the Net Defect Amount exceeds the Defect Threshold, then the
Aggregate Purchase Price shall be reduced by the amount by which the Net Defect
Amount exceeds $10,000,000 (the “Defect Deductible”).

     e. Chevron Corp. Indemnification. Notwithstanding any other provision
hereof, the Aggregate Purchase Price shall not be reduced for Title Defects or
Environmental Defects with respect to the assets of Four Star to the extent that
the Company or its Subsidiaries are entitled to valid and enforceable
indemnification from Chevron Corp. or its controlled affiliates for such Title
Defect(s) or Environmental Defect(s), as the case may be, under the agreements
pursuant to which such assets were sold or contributed to Four Star or its
predecessors (collectively, the “Chevron

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Indemnified Defects”), nor shall the value of the Chevron Indemnified Defects be
included in the Net Defect Amount or considered in determining whether the
Defect Threshold has been met.

     f. Disagreements as to Defect Amount. If the Sellers and the Purchaser are
unable to mutually agree upon the Net Defect Amount at least two business days
prior to the Closing Date, and if the Purchaser’s good faith estimate of the Net
Defect Amount exceeds the Defect Threshold, then at the Closing (1) the portion
of the Aggregate Purchase Price payable at Closing shall be reduced by the
Purchaser’s good faith estimate of the Net Defect Amount minus the Defect
Deductible and (2) the Purchaser shall deliver to an escrow agent mutually
acceptable to the Parties the excess of the Purchaser’s good faith estimates,
over the Sellers’ good faith estimates, of the total reduction to the Aggregate
Purchase Price attributable to Title Defects, Title Benefits, Environmental
Defects and the Net Defect Amount. The disputed Title Defects, Title Benefits,
Environmental Defects and Net Defect Amount shall be resolved post-Closing by
arbitration conducted pursuant to Section 15(f). All amounts escrowed pursuant
to this Section 3(f) shall be distributed by the escrow agent to the Sellers
and/or the Purchaser, and the Aggregate Purchase Price shall be adjusted, in
accordance with the arbitration decision reached in accordance with
Section 15(f).

     g. Post-Closing Curative. Provided that the Net Defect Amount exceeds the
Defect Threshold, the Sellers shall have 90 days following the Closing Date to
attempt to cure any Title Defect or Environmental Defect. Any disputes as to
whether a Title Defect or Environmental Defect has been cured shall be submitted
to arbitration conducted pursuant to Section 15(f). With respect to any Title
Defect or Environmental Defect that the Sellers are able to cure, in whole or in
part, within such 90-day period following the Closing Date, the reduction in the
Aggregate Purchase Price made at Closing with respect to such Title Defect or
Environmental Defect shall be adjusted to reflect such curative, and the Sellers
shall be entitled to periodic distributions from the escrow agent of amounts
related to such cured Title Defects or Environmental Defects. In the event that
the total amount owed to the Sellers as a result of post-closing curatives
pursuant to this Section 3(g) exceeds the total amount deposited with the escrow
agent pursuant to Section 3(f), then the Purchaser shall pay the Sellers the
amount of such excess, and the Purchaser shall cause the release of any amounts
held in escrow to the Sellers, within five business days after the end of the
90-day post-closing cure period (or, if defect disputes are submitted to
arbitration pursuant to Section 15(f), within five business days after the final
decision of the arbitrators). If, at the end of the 90-day post-closing cure
period, the aggregate value of all remaining Title Defects and Environmental
Defects no longer exceeds the Defect Deductible, then the reduction of the
Aggregate Purchase Price for Title Defects and Environmental Defects made at
Closing will be reversed, and (after giving full effect to any distributions
previously made to the Sellers from the escrow account established pursuant to
Section 3(f)) the Purchaser shall pay the full amount of the reduction in the
Aggregate Purchase Price remaining in respect of such Title Defects and
Environmental Defects to the Sellers.

     h. Waiver of Title and Environmental Defects Not Asserted. Subject to the
exception set forth in Section 13(c), the Purchaser waives for all purposes all
objections

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and rights to any adjustment under this Section 3 relating to any Title Defects
or Environmental Defects unless raised by proper notice delivered on or before
the Objection Deadline.

     4. Seller’s Representations And Warranties. Each Seller hereby severally
and not jointly represents and warrants to Purchaser, with respect to
itself/himself/herself, as follows:

     a. Organization and Standing. To the extent Seller is a corporation,
partnership, limited liability company or other business entity formed under the
laws of any state, Seller is duly organized, validly existing and in good
standing under the laws of the state of its organization and in such other
jurisdictions necessary for the consummation of this Agreement.

     b. Power. Seller has all requisite power and authority to carry on its
business as presently conducted and to enter into and perform its obligations
under this Agreement. The execution and delivery of this Agreement does not, and
the fulfillment of and compliance with the terms and conditions hereof will not,
violate, or be in conflict with, any provision of its governing documents, to
the extent applicable, or any provision of any agreement or instrument to which
it is a party or by which it is bound, or to any judgment, decree, order,
statute, rule or regulation applicable to it. No authorizations, consents or
approvals of, or notices to or filings with, any third party or governmental
authority are necessary for the consummation by Seller of the transactions
contemplated hereby, except for such authorizations, consents or approvals as
shall have been obtained or such notices or filings as shall have been accepted
before the Closing Date.

     c. Authorization and Enforceability. The execution, delivery and
performance of this Agreement and the transactions contemplated hereby have been
duly and validly authorized by all requisite actions of the Seller. This
Agreement constitutes the legal, valid and binding obligation of the Seller and
is enforceable in accordance with its terms, subject, however, to the effects of
bankruptcy, insolvency, reorganization, moratorium and other laws for the
protection of creditors generally, as well as to general principles of equity,
regardless of whether such enforceability is considered in a proceeding in
equity or at law.

     d. Title to Shares. Seller owns the Shares shown next to its/his/her name
on Exhibit “B” and, at Closing, will convey to Purchaser good and indefeasible
title to its/his/her Shares free and clear of any and all liens, mortgages,
claims, encumbrances, pledges or security interests and all other defects of
title or other matters whatsoever (other than those arising under federal and
state securities laws).

     e. Liability for Brokers’ Fees. Seller has not incurred any liability,
contingent or otherwise, for brokers’ or finders’ fees relating to the
transactions contemplated by this Agreement for which the Purchaser or the
Company shall have any responsibility.

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     5. Seller’s Representations and Warranties Concerning the Company. Each
Seller hereby severally and not jointly represents and warrants to the Purchaser
that the statements contained in this Section 5 are true and correct as of the
date of this Agreement.

     a. Organization and Standing. The Company and its Subsidiaries are
corporations formed under the laws of the state of Delaware and each such
corporation is (1) duly organized, validly existing and in good standing under
the laws of the state of Delaware and (2) duly qualified to do business as a
foreign corporation and in good standing in each jurisdiction where the
character of the properties owned or leased by it or the nature of its
activities make such qualification necessary.

     b. Power. The Company and its Subsidiaries have all requisite power and
authority to carry on their businesses as presently conducted and to enter into
and perform their obligations under this Agreement. Except as set forth on
Schedule 5(b), the execution and delivery of this Agreement do not, and the
consummation of the transactions contemplated by this Agreement will not:
(1) violate or conflict with any constitution, statute, regulation, rule,
injunction, judgment, order, decree, ruling or other restriction of any
governmental authority or court to which the Company or its Subsidiaries are
subject or any provision of the certificates of incorporation or bylaws of the
Company or its Subsidiaries or any agreement among the stockholders of any such
corporation; or (2) violate, conflict with, result in a breach of, constitute a
default under, result in the acceleration of, create in any party the right to
accelerate, terminate, modify, cancel or receive any payment under, require any
notice of consent under, or result in the imposition of any lien, claim or
encumbrance upon any of the assets of the Company or its Subsidiaries under, any
agreement, contract, lease, license, instrument or other arrangement to which
the Company or its Subsidiaries are a party, by which the Company or its
Subsidiaries are bound or to which the assets of the Company or its Subsidiaries
are subject. Except as set forth on Schedule 5(b), none of the Company or its
Subsidiaries is required to give any notice to, make any filing with, or obtain
any authorization, consent or approval of, any third party or any governmental
authority in order to execute and deliver this Agreement or consummate the
transactions contemplated hereby.

     c. Capitalization. The Company’s authorized capital stock consists of
750,000 shares of which (1) 439,165 shares are authorized as Class A Common
Stock, par value $1.00 per share (“Class A Common Stock”), (2) 24,903 shares are
authorized as Class A-12.5 Common Stock, par value $0.001 per share
(“Class A-12.5 Common Stock”), (3) 35,932 shares are authorized as Class A-25
Common Stock, par value $0.001 per share (“Class A-25 Common Stock”) and
(4) 250,000 shares are authorized as Preferred Stock, par value $1.00 per share,
of which 65,000 shares have been designated Redeemable Convertible Preferred
Stock, Series A (“Series A Preferred Stock”). As of the date hereof, there are
249,359 shares of Class A Common Stock issued and outstanding, 21,168 shares of
Class A-12.5 Common Stock issued and outstanding, 30,542 shares of Class A-25
Common Stock issued and outstanding and 30,012 shares of Series A Preferred
Stock issued and outstanding. In addition, 3,735 shares of authorized but
unissued Class A-12.5 Common Stock and 5,390 shares of authorized but unissued
Class A-25 Common Stock provide the basis for the value of the

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Bonus Plan Payout Amount. The holder of the Series A Preferred Stock holds a
warrant (the “Warrant”) that entitles such holder to purchase 10,000 shares of
Class A Common Stock at the Exercise Price (as defined in the Warrant) in the
event that the Company optionally redeems (as described in Section 5(b) of the
Second Amended and Restated Certificate of Designations of the Company) the
Series A Preferred Stock. All outstanding shares have been validly issued, are
fully paid and non-assessable, were not issued in violation of the terms of any
contract binding upon the Company and were issued in compliance with all
governing documents of the Company. Except as set forth on Schedule 5(c), there
are no outstanding subscriptions, options, warrants, conversion rights,
convertible securities, preemptive rights, preferential rights (contractual or
otherwise) or agreements of any kind for the purchase or sale of equity
securities of the Company or any of its Subsidiaries. At Closing, the Purchaser
will acquire 100% of the issued and outstanding shares of capital stock or other
equity securities of the Company.

     d. Subsidiaries. The Company owns 100% of all of the outstanding capital
stock of Medicine Bow Operating Company, a Delaware corporation, and MBOW Four
Star Corporation, a Delaware corporation.

     e. MBOW Four Star Corporation. The only assets of the Company’s subsidiary,
MBOW Four Star Corporation, are (1) not less than 453 Class A common shares, 215
Class B common shares and 25 Class C common shares, of which 100 common shares
identified herein as Class A common shares are subject to redesignation as
between Class A common shares and Class B common shares, (collectively, the
“Four Star Shares”) of Four Star Oil & Gas Company, a Delaware corporation
(“Four Star”), and (2) those agreements set forth on Schedule 5(e). The Four
Star Shares represent not less than 38.63% of the total outstanding equity
securities of Four Star. No shares of preferred stock or Class B preferred stock
of Four Star are outstanding. MBOW Four Star Corporation has good and
indefeasible title to, and legal and beneficial ownership of, the Four Star
Shares, free and clear of any and all liens, mortgages, claims, encumbrances,
other pledges or security interests and all other defects of title or other
matters whatsoever other than (1) any obligations that arise under the Four Star
Stockholders Agreement or the Credit Facility and (2) those arising under
federal and state securities laws. Except as set forth on Schedule 5(e), there
are no outstanding subscriptions, options, warrants, conversion rights,
convertible securities, preemptive rights, preferential rights (contractual or
otherwise) or agreements of any kind for the purchase or sale of equity
securities of MBOW Four Star Corporation. At Closing, the Purchaser will own
100% of the issued and outstanding equity securities of MBOW Four Star
Corporation.

     f. Financial Statements. Attached hereto as Schedule 5(f) are the following
financial statements (collectively, the “Financial Statements”): (1) audited
consolidated balance sheets of the Company and its Subsidiaries as of
December 31, 2004 and 2003, and the related consolidated statements of
operations, shareholders’ equity, and cash flows of the Company and its
Subsidiaries for the year ended December 31, 2004; and (2) an unaudited
consolidated balance sheet of the Company as of June 30, 2005, and related
consolidated statements of operations and cash flows for the six months then
ended (the “Most Recent Period End”). The Financial Statements at and for the
six-month period

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ended June 30, 2005, are herein referred to as the “Most Recent Financial
Statements.” The Financial Statements (including the notes thereto) have been
prepared in accordance with GAAP in all material respects applied on a
consistent basis throughout the periods covered thereby and present fairly, in
all material respects, the consolidated financial position of the Company and
its Subsidiaries as of such dates and the results of operations for such
periods, and are consistent with the books and records of the operations for
such periods, and are consistent with the books and records of the Company;
provided, however, that the Most Recent Financial Statements are subject to
normal year-end adjustments and lack footnotes and other presentation items.

     g. Events Subsequent to Most Recent Period End. Since the date of the Most
Recent Financial Statements, excluding distributions made to the holders of the
Class A Preferred Stock in the ordinary course, there have not been any
(1) distributions by the Company to the holders of its equity securities or
(2) changes in the assets, condition, affairs (financial or otherwise) or
business prospects of the Company and its Subsidiaries, taken as a whole, which
have had or would be reasonably likely to have, individually or in the
aggregate, a Material Adverse Effect.

     h. Legal Compliance. Except as set forth on Schedule 5(h), the Company and
each of the Subsidiaries (1) are in substantial compliance with all applicable
laws (including rules, regulations, codes, plans, injunctions, judgments,
orders, decrees, rulings, and charges thereunder) and (2) have or have timely
applied for all permits, licenses, certificates of authority, orders and
approvals of, and have made all filings and applications with, federal, state,
and local regulatory bodies required to carry on their current operations in the
ordinary course of business.

     i. Tax Matters.

     I. Except as set forth on Schedule 5(i), the Company, each of its
Subsidiaries and each affiliated, consolidated, combined or unitary group of
which the Company or any of its Subsidiaries is or has been a member (an
“Affiliated Group”), has filed timely with the appropriate taxing authorities
all Tax Returns required to be filed by the Company, its Subsidiaries or any
Affiliated Group. Each such Tax Return is true, correct and complete in all
material respects. All Taxes of the Company and its Subsidiaries that are due
and payable have been timely paid in full. The unpaid Taxes of the Company and
its Subsidiaries did not, as of the Most Recent Period End, exceed the reserve
for Tax liability (excluding any reserve for deferred Taxes established to
reflect timing differences between book and Tax income) set forth or included in
the Most Recent Financial Statements, and do not exceed the reserve as adjusted
for passage of time through the Closing Date in accordance with the past custom
of the Company and its Subsidiaries in filing their Tax Returns.

     II. There is no action, suit, proceeding, investigation, audit, claim or
assessment pending or threatened with respect to the Company or its Subsidiaries
with respect to a liability for Taxes or with respect to any Tax Return. No
deficiency for any Tax has been assessed with respect to the Company or its

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Subsidiaries which has not been paid in full. There are no liens for Taxes upon
the assets or properties of the Company or its Subsidiaries other than liens for
Taxes not yet due and payable and for which adequate reserves have been
established in the Financial Statements.

     III. Each of the Company and its Subsidiaries has withheld and timely paid
all Taxes required to have been withheld and paid in connection with amounts
paid or owing to any employee, independent contractor, creditor, member or other
third party.

     IV. There are no outstanding waivers or comparable consents regarding the
application of the statute of limitations with respect to any Taxes or Tax
Returns of the Company or its Subsidiaries.

     V. None of the Company or its Subsidiaries is a party to, is bound by, or
has any obligation under, any Tax sharing agreement, Tax indemnification
agreement or similar contract or arrangement, and none of the Company or its
Subsidiaries has any potential liabilities or obligations to any Person as a
result of, or pursuant to, any such agreement, contract or arrangement. None of
the Company or its Subsidiaries has any liability for Taxes of another Person by
contract or otherwise.

     j. Material Agreements. Schedule 5(j) lists all (1) governing documents of
the Company and its Subsidiaries (including, without limitation, certificates of
incorporation, certificates of designation, bylaws, stockholder agreements,
investor rights agreements and other similar instruments), (2) contracts with
Persons who will be affiliates of the Company immediately prior to Closing that
will be binding on the Company or its Subsidiaries (or the assets of the Company
or its Subsidiaries) after Closing, (3) agreements for the sale or purchase of
hydrocarbons produced from or attributable to the assets of the Company or its
Subsidiaries, except for agreements that expire by their terms or may be
terminated without penalty within 30 days after the Closing Date,
(4) instruments that create any area of mutual interest, except for areas of
mutual interest created under joint operating agreements, (5) instruments that
create or evidence an asset purchase or sale agreement that has not been
consummated as of the date hereof, (6) contracts to which the Company or any
Subsidiary is a party, the performance of which will involve consideration in
excess of $100,000.00 per year or (7) any other agreement not described in
(1) through (6) above the existence or loss of which has had or would be
reasonably likely to have a Material Adverse Effect (collectively, the “Material
Agreements”). The Company has made available to the Purchaser a copy of each
Material Agreement and all minute books of the Company and its Subsidiaries, the
copies of which are true, accurate and complete in all material respects. With
respect to each Material Agreement, the Company is not in breach or default of
the terms and conditions of such agreement.

     k. Litigation. Schedule 5(k) sets forth each instance in which the Company
or any Subsidiary (1) is subject to any outstanding injunction, judgment, order,
decree, ruling, or charge, or (2) is a party to any action, suit, proceeding,
hearing, or investigation

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of, in, or before any court or quasi judicial or administrative agency of any
jurisdiction, or (3) has been threatened to be sued or made a party to any such
proceeding.

     l. Liability for Brokers’ Fees. Except as set forth on Schedule 5(l),
neither the Company nor its Subsidiaries have incurred any liability, contingent
or otherwise, for brokers’ or finders’ fees relating to the transactions
contemplated by this Agreement for which the Purchaser or the Company shall have
any responsibility.

     m. Insurance. Schedule 5(m) describes all contracts of insurance maintained
by the Company, which are in full force and effect, and all premiums due and
owing in connection with such policies have been paid. The Company has given
notice or has otherwise presented every material claim known to the Company to
be covered by insurance under its insurance policies or contracts in a timely
fashion.

     n. Labor Matters and Employee Benefit Plans. Except as shown on Schedule
5(n) hereto:

     I. Schedule 5(n)(I) lists all Benefit Plans. With respect to each such
Benefit Plan, Seller has made available to Purchaser true and accurate copies of
(1) the most recent plan documents and any amendments thereto, (2) the most
recent summary plan description and all related summaries of material
modification and (3) for any Benefit Plan intended to be qualified under Section
401(a) of the Code, (A) a copy of the most recent annual report (Form 5500
Series) filed with the IRS and (B) the most recent favorable determination
letter received from the IRS. All Benefit Plans and their related trusts have
been and are maintained in accordance with each such plan’s terms and in
operation in compliance with the requirements of all applicable federal and
state statutes and regulations. Each Benefit Plan intended to be qualified under
Section 401 of the Code has received a favorable determination or opinion
letter(s) from the IRS as to its qualified status, and no fact or event has
occurred since the date of such letter(s) that could reasonably be expected to
adversely affect the qualified status of any such Benefit Plan. Each of the
Benefit Plans can be terminated in accordance with its terms and without
liability to the Company or any of its Subsidiaries other than for ordinary
administration expenses, benefits accrued or, with respect to welfare benefit
plans, claims incurred thereunder through the date of such termination, and the
transactions contemplated by this Agreement will not result in the imposition of
any restrictions, limitations or penalty on the right to amend or terminate any
Benefit Plan.

     II. Neither the Company nor any ERISA Affiliate has ever established,
maintained, contributed to or had any liability or obligation to contribute to
(1) any pension plan that is subject to section 412 of the Code or Title IV of
ERISA, (2) any multiemployer plan within the meaning of Section 3(37) of ERISA
or (3) any Benefit Plan providing medical, health, or other welfare-type
benefits for retired or terminated Company Employees other than in accordance
with COBRA or any similar state or local laws.

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     III. The Company is not a party to, nor has it ever been a party to, any
collective bargaining agreement.

     IV. Except pursuant to the Company’s 2004 Equity Incentive Plan as
described in Section 7(b), the execution and delivery of, and the performance of
the transactions contemplated by, this Agreement will not (either alone or upon
the occurrence of any additional or subsequent events) constitute an event under
any Benefit Plan, trust or loan that will or may result in any payment (whether
of severance pay or otherwise), acceleration, forgiveness of indebtedness,
vesting, distribution, increase in benefits or obligation to fund benefits with
respect to any current or former employee of the Company or its Subsidiaries.

     V. The Company has made no agreement with any Person, including, but not
limited to, the holders of the Class A-12.5 Common Stock and the Class A-25
Common Stock and participants in the Bonus Pool regarding the tax treatment of
the Class A-12.5 Common Stock, the Class A-25 Common Stock or amounts received
in respect of the Bonus Plan Payout Amount, nor does the Company have any
obligation to “gross-up” any Person, including, but not limited to, the holders
of the Class A-12.5 Common Stock and the Class A-25 Common Stock and
participants in the Bonus Pool for any income or excise tax or penalty that may
be imposed on such Person.

     o. Credit Facility. Since the date of the Most Recent Financial Statements,
the Company has not made any borrowings under its Credit Facility except for
borrowings (1) in the ordinary course of business or (2) for items described on
Schedule 5(o).

     p. Hedging Transactions. Schedule 5(p) sets forth all obligations
(including, without limitation, any obligations relating to the posting of
collateral and the actual amounts posted as collateral, whether in the form of
cash, letters of credit or otherwise, in respect of such obligations) of the
Company and its Subsidiaries (collectively, “Hedge Obligations”) in respect of
any futures, hedges, swaps, collars, puts, calls, floors, caps, options, forward
sales, forward purchases or other contracts or derivative securities that are
intended to benefit from, relate to or reduce or eliminate the risk of
fluctuations in the price of commodities (including, without limitation,
hydrocarbons), interest rates, currencies or securities (collectively, “Hedge
Transactions”). The Company and its Subsidiaries are not in breach or violation
of any Hedge Obligation. The Company and its Subsidiaries have not entered into
any Hedge Transaction for the purposes of speculation.

     q. Gas Imbalances. Except as set forth on Schedule 5(q), (1) there are no
aggregate production, pipeline transportation or processing imbalances or
penalties existing with respect to the Company, its Subsidiaries or their oil
and gas properties and interests (collectively, “Operating Interests”) and
(2) neither the Company nor its Subsidiaries have received a deficiency payment
under any gas contracts for which any party has a right to take deficiency gas
from the Company or its Subsidiaries, nor have

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the Company or its Subsidiaries received any payments for production which are
subject to refund or recoupment out of future production.

     r. Prepaid Gas Obligations. Except as set forth on Schedule 5(r), neither
the Company nor its Subsidiaries are subject to any “take or pay” arrangement,
production payment arrangement, gas balancing agreement (other than under joint
operating agreements) or otherwise required to deliver or to suffer the delivery
of hydrocarbons produced in connection with any of the Operating Interests at
some future time (or make a cash payment in lieu thereof) without then or
thereafter receiving full payment therefor and without deduction or credit on
account of such arrangement from the price that would otherwise be received.

     s. Preferential Rights; Restrictions on Transfer. Except as set forth on
Schedule 5(s), there are no preferential rights to purchase or other similar
rights or restrictions on assignment, including requirements for consents from
third parties to assignment, affecting the Operating Interests or Wells that
would be applicable to, or required for the consummation of, the transactions
contemplated by this Agreement, and the transactions contemplated by this
Agreement will not create in any individual or entity any option to purchase,
preferential right to purchase or similar rights with respect to the Operating
Interests.

     t. Calls on Production. Except as set forth on Schedule 5(t), there are no
calls on production (whether or not exercised) or other similar marketing
restrictions affecting the Operating Interests, nor will the transactions
contemplated by this Agreement create any such calls on production.

     u. No Undisclosed Liabilities. Except for liabilities incurred or paid (1)
after the date of the Most Recent Financial Statements but before the date of
this Agreement and (2) after the date of this Agreement that do not violate
Section 8, there are no liabilities, debts or obligations of the Company or its
Subsidiaries of any kind, whether accrued, absolute, contingent, inchoate or
otherwise (and there is no basis for any present or future action, suit,
proceeding, hearing, investigation, charge, complaint, claim or demand against
the Company or its Subsidiaries giving rise to any such debt, liability or
obligation) including any taxes which are due and payable as of the date hereof
or any governmental charges or penalties, interest or fines, except for
liabilities (A) reflected on or reserved against in the Financial Statements or
otherwise disclosed in the notes thereto or (B) set forth on Schedule 5(u).

     v. No Known Material Adverse Effects with Regard to Four Star. To the
knowledge of the Sellers, since the date of the Most Recent Financial
Statements, there has not been, with respect to the oil and gas properties and
operations of Four Star, any fact, circumstances or events which, individually
or in the aggregate, would constitute a Material Adverse Change nor will the
transactions contemplated by this Agreement violate any governing documents of
Four Star of which the Sellers are actually aware (including, without
limitation, its certificate of incorporation, the certificates of designations
for its preferred shares, its bylaws or its stockholders agreement) or any

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agreements relating to Four Star (1) as to which MBOW Four Star Corporation is a
party and (2) of which the Sellers are actually aware.

     6. Purchaser’s Representations. Purchaser represents and warrants to
Sellers and Company as of the date hereof and at Closing as follows:

     a. Organization and Standing. Purchaser is a corporation, formed under the
laws of the state of Delaware, and is duly organized, validly existing and in
good standing under the laws of Delaware and in such other jurisdictions
necessary for the consummation of this Agreement.

     b. Power. Purchaser has all requisite power and authority to carry on its
business as presently conducted and to enter into this Agreement. The execution
and delivery of this Agreement does not, and the fulfillment of and compliance
with the terms and conditions hereof will not, as of Closing, violate, or be in
conflict with, any material provision of its governing documents, when
applicable, or any material provision of any agreement or instrument to which it
is a party or by which it is bound, or to any judgment, decree, order, statute,
rule or regulation applicable to it. Except for the actions described in
Section 7(c), the Purchaser is not required to give any notice to, make any
filing with, or obtain any authorization, consent or approval of, any third
party or any governmental authority in order to execute and deliver this
Agreement or consummate the transactions contemplated hereby.

     c. Authorization and Enforceability. The execution, delivery and
performance of this Agreement and the transactions contemplated hereby have been
duly and validly authorized by all requisite action of the Purchaser and its
parent, if any. This Agreement constitutes the legal, valid and binding
obligation of the Purchaser, and is enforceable in accordance with its terms,
subject, however, to the effects of bankruptcy, insolvency, reorganization,
moratorium and other laws for the protection of creditors generally, as well as
to general principles of equity, regardless whether such enforceability is
considered in a proceeding in equity or at law.

     d. Acquisition Not for Distribution Purposes. Purchaser is acquiring the
Shares for investment purposes and not with a view to distribution.

     e. Restriction on Transfers. Purchaser acknowledges that the Shares are not
registered under the Securities Act of 1933, as amended. Purchaser will not
sell, transfer or otherwise dispose of the Shares in violation of the Securities
Act of 1933, as amended, the Securities Exchange Act of 1934, as amended, or the
rules promulgated thereunder, including Rule 144 under the Securities Act of
1933, as amended.

     f. Funding. The Purchaser has available and will have available at Closing
adequate funds or the means to obtain adequate funds in an aggregate amount
sufficient to pay (1) all amounts required to be paid by the Purchaser under
this Agreement and (2) all expenses which have been or will be incurred by the
Purchaser in connection with this Agreement and the consummation of the
transactions contemplated hereby.

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     g. Liability for Brokers’ Fees. Purchaser has not incurred any liability,
contingent or otherwise, for brokers’ or finders’ fees relating to the
transaction contemplated by this Agreement for which any Seller shall have any
responsibility.

     7. Covenants.

     a. Independent Evaluation; Access. Purchaser is experienced and
knowledgeable in the oil and gas business. Purchaser is aware of risks
associated with the oil and gas business and, specifically, the Company’s and
Four Star’s business, operations and assets and has formed its own judgment as
to the value of the Shares. Purchaser is relying upon its own judgment and
decision in entering into and consummating the transaction. Between the
execution date and the Closing Date, the Company shall use commercially
reasonable efforts, upon the request of the Purchaser, to assist Purchaser in
the examination of the files, records, weekly accounts payable check runs,
minute books, information and data regarding the business of the Company and its
Subsidiaries and the records, information and data in the Company’s possession
regarding Four Star (collectively, the “Records”), in addition to information
that is available to the public. Except as provided in Section 5(j), Purchaser
acknowledges and agrees that neither the Company nor its Subsidiaries,
directors, officers or employees nor Sellers have made any representations or
warranties, express or implied, written or oral, as to the accuracy of the
Records. Except for the representations and warranties of Sellers contained in
this Agreement, Sellers have not made any representation or warranty to
Purchaser including any estimate with respect to the value of the assets of the
Company, its Subsidiaries or Four Star or reserves or any projections as to
events that could or could not occur. In entering into this Agreement, Purchaser
acknowledges and affirms that it has relied and will rely solely on the terms,
representations and warranties of this Agreement and upon its independent
analysis, evaluation and investigation of, and judgment with respect to, the
business, economic, legal, tax or other consequences of this transaction
including its own estimate and appraisal of the extent and value of the
petroleum, natural gas and other reserves attributable to the assets of the
Company, its Subsidiaries and Four Star. Purchaser’s representatives will be
given full access and the opportunity to conduct a Phase I Environmental
Inspection and equipment inventory and to visit with personnel and physically
examine the assets and operations of the Company and its Subsidiaries. Purchaser
may not conduct testing or sampling of soil, ground water, surface water or
other media or materials during such inspection without the prior written
consent of the Majority of Sellers, such consent not to be unreasonably withheld
or delayed. No Seller shall have any liability to Purchaser or its affiliates,
agents, representatives or employees resulting from any use, authorized or
unauthorized, of the Records or other information relating to the Company, its
Subsidiaries or Four Star. Nothing contained in this Section 7(a) shall serve to
mitigate or modify the operation of Section 3 or the scope or effect of the
representations and warranties set forth in Section 4 or Section 5 in any
respect.

     b. Treatment of Equity Incentive Plan. The Sellers and the Company agree
that the Company’s 2004 Equity Incentive Plan provides for cash bonus payments
to participants in the Bonus Pool in an aggregate amount equal to the value of
the Authorized But Unissued Class A-12.5 Common Stock and Authorized But
Unissued

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Class A-25 Common Stock, as such terms are defined and determined pursuant to
the Company’s 2004 Equity Incentive Plan. Prior to the Closing, the Company
shall determine the value of the Bonus Plan Payout Amount and the allocation of
the Bonus Plan Payout Amount to the individual participants in the Bonus Pool
accordance with the terms and conditions of the Company’s 2004 Equity Incentive
Plan, and the Company shall provide such allocation to the Purchaser at least
two business days prior to Closing. Sellers shall use commercially reasonable
efforts to cause (1) the Company’s 2004 Equity Incentive Plan to be cancelled
simultaneous with the Closing, and (2) the holders of Class A-12.5 Common Stock
and Class A-25 Common Stock and the participants in the Bonus Pool to have no
further rights under the Company’s 2004 Equity Incentive Plan other than the
right to receive the consideration provided for by this Agreement on the Closing
Date. To the extent that any payment to a participant in the Company’s 2004
Equity Incentive Plan could reasonably be expected to be an “excess parachute
payment” to a “disqualified individual” as such terms are defined in
Section 280G of the Code, the Sellers agree to use their reasonable best efforts
to obtain, prior to the Closing, the agreement of the individuals otherwise
entitled to receive such payment that (1) neither the Purchaser nor the Company
will have any obligation to make such payment and (2) such payment will not be
made, in each case absent stockholder approval upon full disclosure pursuant to
the requirements of Section 280G(b)(5) and the regulations issued pursuant
thereto.

     c. HSR Clearance. Upon execution of this Agreement, and to the extent
applicable, both Parties (and, to the extent appropriate, El Paso Corporation)
as promptly as possible shall file with the Federal Trade Commission and/or the
Department of Justice, as applicable, the required notification and report forms
due under the Hart-Scott-Rodino Antitrust Improvement Acts of 1976 (“HSR Act”)
and shall as promptly as practicable furnish any supplemental information that
may be requested in connection therewith. Each Party (and, to the extent
appropriate, El Paso Corporation) shall take all reasonable steps to achieve
early termination of applicable HSR Act waiting periods. To the extent required,
the Company shall use its commercially reasonable efforts to cause Four Star to
provide all information and make all filings required to be provided or made by
Four Star to secure the requisite approvals under the HSR Act. The cost of all
filings by the Parties pursuant to the HSR Act shall be borne 50% by the Company
and 50% by the Purchaser.

     d. Termination of Subscription Agreement and Cancellation of Warrant. On
the Closing Date, the Company and each Seller that is a party to the
Subscription Agreement shall enter into an agreement to terminate the
Subscription Agreement, and the holder of the Warrant shall deliver the
unexercised Warrant, stamped “CANCELLED,” to the Purchaser at the Closing.

     e. Series A Preferred Stock and Warrant. In compliance with the certificate
of designations governing the Series A Preferred Stock, the Company shall not
optionally redeem any shares of Series A Preferred Stock. In compliance with the
terms of the Warrant, the holder of the Warrant shall not exercise any portion
thereof.

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     f. Assignment of Certain Leases. The Company and Medicine Bow Operating
Company are the beneficial owners of certain oil and gas leases which have been
acquired on their behalf by brokers or agents. Each of the Company and Medicine
Bow Operating Company shall use commercially reasonable efforts to cause its
brokers and agents to deliver recordable assignments of such oil and gas leases
to the Company or Medicine Bow Operating Company, as the case may be, prior to
Closing.

     g. Notifications by Purchaser of Breach. To the extent that the Purchaser
actually becomes aware, prior to Closing, of breaches of the representations set
forth in Section 4 and Section 5 that would, in the Purchaser’s reasonable
judgment, collectively constitute a Material Adverse Change, then the Purchaser
shall promptly notify the Sellers of such discovery.

     8. Operation of Business. From the date hereof until the Closing Date, the
Company will not, without the written consent of Purchaser (which consent shall
not be unreasonably withheld, conditioned or delayed), except as expressly
contemplated by this Agreement, engage in any practice, take any action, or
enter into any transaction outside the ordinary course of business. Without
limiting the generality of the foregoing, from the date hereof until the Closing
Date, the Company will not, without the written consent of Purchaser (which
consent shall not be unreasonably withheld, conditioned or delayed), do any of
the following:

     a. amend or otherwise change its charter or bylaws or equivalent governing
documents;

     b. make or commit to make any capital expenditure or group of related
capital expenditures in excess of $100,000.00 individually or $500,000.00 in the
aggregate that is not provided for in the Company’s June 30, 2005 Reserve Report
provided to the Purchaser;

     c. issue, sell, pledge, dispose of, grant, encumber or authorize the
issuance, sale, pledge, disposition, grant or encumbrance of (1) any shares of
capital stock of any class of the Company or any Subsidiary, or any options,
warrants, convertible securities or other rights of any kind to acquire any
shares of such capital stock, or any other ownership interest (including,
without limitation, any phantom interest), of the Company or any Subsidiary, or
(2) any assets and properties material to the Company, except for (A) sales of
oil, gas, or natural gas liquids in the ordinary course of business, or
(B) pledges of assets and properties required by any financing documents to
which the Company is a party on the date hereof;

     d. acquire or dispose of (including, without limitation, by merger,
consolidation or acquisition of stock or assets) any corporation, partnership or
other business organization or any division thereof or any material amount of
assets, except for acquisitions of assets having an aggregate fair market value
of less than $500,000.00 in the ordinary course of business;

     e. incur any indebtedness for borrowed money or issue any debt securities
or assume, guarantee or endorse, or otherwise as an accommodation become
responsible for,

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the obligations of any individual or entity, or make any loans or advances,
except borrowings under the Credit Facility consistent with Exhibit “D”;

     f. increase the compensation payable or to become payable to, or grant any
severance or termination pay to, its officers, employees, directors or
consultants, except pursuant to existing contractual arrangements, or existing
compensation plans, or enter into any employment, consulting or severance
agreement with, any director, officer or other employee or consultant of the
Company, or establish, adopt, enter into or amend any collective bargaining,
bonus, profit sharing, compensation, stock option, restricted stock (except
pursuant to the Company’s 2004 Equity Incentive Plan as described in
Section 7(b)), pension, retirement, deferred compensation, employment,
termination, severance or other plan, agreement, trust, fund, policy or
arrangement for the benefit of any director, officer, employee or consultant
except, in each case, for actions resulting from the normal application of the
Company’s policies, consistent with past practice;

     g. except for distributions made to holders of shares of Series A Preferred
Stock in the ordinary course, declare, set aside or pay any dividend or make any
other distribution to shareholders;

     h. amend in any material respect any Material Agreement or terminate any
Material Agreement prior to the expiration of the term thereof;

     i. commence or file any action, suit, or proceeding before any court or
governmental agency or authority, or enter into any consent or settlement with
respect to any action, claim, proceeding, litigation or investigation, in each
case other than in the ordinary course of business;

     j. pay, discharge or satisfy any material claims, liabilities or
obligations (absolute, accrued, contingent or otherwise) other than (1) the
payment, discharge or satisfaction in the ordinary course of business of
liabilities reflected or reserved against on the Financial Statements,
(2) payments under the Credit Facility or (3) payments of current liabilities
(A) in the ordinary course of business and (B) consistent with the Current
General and Administrative Budget of the Company set forth in Exhibit “D”, in
each case which do not bestow any personal benefits to the directors, officers,
employees, stockholders or affiliates of the Company or its Subsidiaries that
are materially inconsistent with past benefits bestowed on such individuals or
entities;

     k. make or change any tax election or change any method of accounting or
accounting practice;

     l. introduce any methods of management or operation with respect to any or
all of the Operating Interests that are materially inconsistent with past
practices;

     m. voluntarily relinquish its position as operator of any Well or abandon
any Well other than as required by law or contract;

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     n. enter into any agreement or arrangement transferring, selling or
encumbering any of the Operating Interests (other than pursuant to any
agreements or arrangements existing on the date hereof);

     o. enter into any new sales contract or supply contract which cannot be
cancelled on 30 days’ prior notice;

     p. enter into any financing lease obligation; or

     q. commit or agree to any of the foregoing.

In furtherance of the foregoing, the Purchaser shall periodically make available
to the Company a representative of the Purchaser, and the Company shall provide
work space in its principal corporate offices during its normal business hours
for a representative of the Purchaser, which Purchaser representative will
facilitate any consent required by the Purchaser hereunder. The Company agrees
that it will promptly inform such Purchaser representative of any practices,
activities or transactions that might require consent by the Purchaser hereunder
and will afford such Purchaser representative reasonable access to any books and
records necessary for such consent to be made on an informed basis.

     9. Further Assurances. Subject to the terms and conditions herein provided,
each Party shall take, or cause to be taken, all actions and shall do, or cause
to be done, all things necessary, appropriate or desirable under any applicable
laws or under applicable governing agreements to consummate and make effective
the transactions contemplated by this Agreement, including using reasonable
efforts to obtain all necessary waivers, consents and approvals and effecting
all necessary registrations and filings. Each Party shall take, or cause to be
taken, all action or shall do, or cause to be done, all things necessary,
appropriate or desirable to cause the covenants and conditions applicable to the
transactions contemplated hereby to be performed or satisfied as soon as
practicable. In addition, if any governmental authority shall have issued any
order, decree, ruling or injunction, or taken any other action that would have
the effect of restraining, enjoining or otherwise prohibiting or preventing the
consummation of the transactions contemplated hereby, each of the Parties shall
use reasonable efforts to have such order, decree, ruling or injunction or other
action declared ineffective as soon as practicable. With respect to all actions
required to be taken by the Company pursuant to this Agreement (including,
without limitation, under Section 7, Section 8 and this Section 9), each of the
Sellers shall take, or cause to be taken, all action and shall do, or cause to
be done, all things necessary, appropriate or desirable to cause the Company to
take those actions. Subsequent to the Closing, each Seller, without the
necessity of any further consideration whatsoever, will execute and deliver such
further instruments and take such additional actions as the Purchaser may
reasonably request to confirm or further evidence the transactions contemplated
hereby. In addition to the foregoing, the Company shall use its reasonable
efforts in conjunction with the Purchaser’s efforts to cause those individuals
who serve an accounting or finance function at the Company and the Company’s
independent accountants to assist the Purchaser, at the Purchaser’s expense, in
preparing the pro forma financial information that will be required to be filed
by the Purchaser on Form 8-K/A after the consummation of the transactions
contemplated by this Agreement.

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     10. Conditions to Proceed with Closing. The obligation of the Parties to
proceed with Closing shall be subject to the satisfaction or waiver, on or
before the Closing Date, of the following conditions:

     a. Conditions to the Parties’ Obligation to Proceed with Closing. The
obligation of the Sellers and Purchaser to proceed with Closing shall be subject
to the satisfaction or waiver, on or before the Closing Date, of the following
condition: all authorizations, consents, orders, declarations or approvals of,
or filings with or terminations or expirations of waiting periods imposed by
(including, without limitation, expiration of any waiting period pursuant to the
HSR Act), any governmental entity or regulatory authority, which the failure to
obtain, make or occur would have the effect of making the transactions
contemplated by this Agreement illegal or would have (or would be reasonably
likely to have) a Material Adverse Effect on the Company or the Purchaser
assuming the transactions contemplated by this Agreement had taken place, shall
have been obtained, made or occurred on or before the Closing Date.

     b. Conditions to the Purchaser’s Obligation to Proceed with Closing. The
obligation of the Purchaser to proceed with Closing shall be subject to the
satisfaction or waiver, on or before the Closing Date, of the following
conditions:

     I. Ownership Representations. The representations and warranties set forth
in Section 4(d), Section 5(c), Section 5(d) and Section 5(e) (the “Ownership
Representations”) and in Section 5(v) shall be true and correct in all respects
at Closing.

     II. Covenant Compliance. The Company and the Sellers shall have complied in
all material respects with those covenants contained in this Agreement that are
applicable to them.

     III. Non-Ownership Representations. Except for (1) the Ownership
Representations and (2) the representation and warranty set forth in Section
5(v), all of the representations and warranties set forth in Section 4 and
Section 5 (collectively, the “Non-Ownership Representations”) shall be true and
correct in all respects at Closing, except to the extent that the circumstances
causing the Non-Ownership Representations not to be true and correct in all
respects (disregarding all qualifications contained therein regarding
materiality) would not, individually or in the aggregate, constitute a Material
Adverse Change.

     IV. 100% Delivered. The Sellers shall be in a position to deliver 100% of
the issued and outstanding equity securities of the Company to the Purchaser
pursuant to Section 11(a)(I).

     V. Seller Certificates. The Purchaser shall have received from each Seller
an unqualified certificate covering those items addressed in Section 11(a)(II).

     VI. Legal Opinions. The Purchaser shall have received a legal opinion or
legal opinions from counsel reasonably acceptable to the Purchaser, in form

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and substance reasonably satisfactory to the Purchaser and its counsel, as to
the due authorization of the Person executing this Agreement on behalf of each
Seller that is an entity to execute and deliver this Agreement on behalf of such
Seller, such opinions to be substantially in the form of Exhibit “E”.

     VII. Waiver/Release from Equity Plan Participants. Each participant in the
Company’s 2004 Equity Incentive Plan (including each participant in the Bonus
Pool and each holder of shares of Class A-12.5 Common Stock or Class A-25 Common
Stock) shall have delivered to the Purchaser and the Company a full waiver and
release, in form and substance reasonably satisfactory to the Purchaser, of any
claims arising under the Company’s 2004 Equity Incentive Plan effective upon the
Closing.

     VIII. Resignations. Each director and officer of the Company and its
Subsidiaries shall have delivered to the Purchaser a letter of voluntary
resignation from such positions with the Company and its Subsidiaries effective
as of the Closing (and, in the case of any officer party to an employment
agreement with the Company, such letter shall acknowledge that such resignation
constitutes a termination of such agreement by the employee “without cause” for
purposes of such agreement). Each director of Four Star designated by MBOW Four
Star Corporation shall have delivered a letter of voluntary resignation from
such position with Four Star effective upon the Closing.

     IX. Casualty Loss. No Operating Interests, Wells or other oil and gas
interests of the Company, its Subsidiaries or Four Star shall have been
destroyed by any natural event (including, without limitation, any storm, flood,
hurricane, washout, landslide, earthquake, lightning, fire or other act of God)
or other casualty or been taken in condemnation or under right of eminent
domain, except for such destructions, casualties or takings as would not,
individually or in the aggregate, constitute a Material Adverse Change.

     X. Environmental Compliance. Except for Environmental Defects arising
before the Objection Deadline, and except as would not, individually or in the
aggregate, constitute a Material Adverse Change, the Company and its
Subsidiaries shall (1) be in possession of all Environmental Approvals needed to
carry on their current operations, (2) be in compliance with all Environmental
Laws and (3) not have received any demand or notice with respect to any
non-compliance with Environmental Laws.

     XI. Remedial HSR Act Filings. The Company shall have made all filings with
the Federal Trade Commission and/or the Department of Justice, as applicable,
under the HSR Act as shall be required, in the Purchaser’s reasonable judgment,
to remedy potential failures to file in respect of historic acquisitions of a
portion of the Four Star Shares, and such remedial filings shall have been
accepted by the Federal Trade Commission and/or the Department of Justice,
except to the extent such non-acceptance would not constitute a Material Adverse
Change.

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     XII. Financial Advisor Acknowledgments. Petrie Parkman & Co. shall have
executed and delivered to the Purchaser a letter acknowledging that (1) all
amounts owed by the Company to Petrie Parkman & Co. in connection with the
transactions contemplated by this Agreement pursuant to the engagement letter
between Petrie Parkman & Co. and the Company dated as of April 7, 2005
(excluding any amounts owed in respect of unreimbursed out-of-pocket expenses)
have been paid at Closing and (2) no other amounts will be owed by the Company
to Petrie Parkman & Co. (except for any amounts owed in satisfaction of any
indemnification obligation arising under the engagement letter dated as of
April 7, 2005) in respect of any future transactions, whether pursuant to the
aforementioned engagement letter or otherwise. Rivington Capital Advisors, LLC
shall have executed and delivered to the Purchaser a letter acknowledging that
(1) all amounts owed by the Company to Rivington Capital Advisors, LLC in
connection with the transactions contemplated by this Agreement or any
transactions consummated prior to Closing pursuant to the engagement letters
between Rivington Capital Advisors, LLC and the Company dated as of April 7,
2005 and April 29, 2005 (excluding any amounts owed in respect of unreimbursed
out-of-pocket expenses) have been paid at or prior to Closing and (2) no other
amounts will be owed by the Company to Rivington Capital Advisors, LLC (except
for any amounts owed in satisfaction of any indemnification obligation arising
under the engagement letters dated as of April 7, 2005 and April 29, 2005) in
respect of any future transactions, whether pursuant to the aforementioned
engagement letters or otherwise.

     XIII. Spousal Consents. The spouse of each Seller that is an individual
shall have executed and delivered to the Purchaser a written instrument
substantially the form attached hereto as Exhibit “F”.

     XIV. Peters Consent. Oscar L. Peters shall have executed and delivered to
the Purchaser a written instrument acknowledging that, for purposes of the
letter agreement between the Company and Mr. Peters dated as of January 7, 2005,
the transactions contemplated by this Agreement shall not constitute a “Change
of Control” that would entitle Mr. Peters to any lump-sum payment from the
Company. Notwithstanding the foregoing, it is the understanding of the Parties
that (1) the Equity Incentive Committee under the Company’s 2004 Equity
Incentive Plan will cause Mr. Peters to participate in the Bonus Plan Payout
Amount to the full extent of the lump-sum payment to which he would have been
entitled upon a “Change of Control” under the aforementioned letter agreement
and (2) if Mr. Peters fails to deliver the written instrument described in the
preceding sentence, then the condition to closing set forth in this
Section 10(b)(XIV) shall be satisfied if the Aggregate Purchase Price is reduced
by the amount of the lump-sum payment to which Mr. Peters will be entitled under
the aforementioned letter agreement as a result of the consummation of the
transactions contemplated by this Agreement.

     XV. Extension of Services Agreement. The Company shall have delivered to
the Purchaser a written agreement, signed on behalf of both Texaco

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Exploration and Production Inc. (or any other appropriate controlled affiliate
of Chevron Corp.) and Four Star, extending that certain Services Agreement,
dated as of November 1, 1999 (the “Services Agreement”), between Texaco
Exploration and Production Inc. and Four Star, through December 31, 2005, which
extension shall be on terms consistent in all material respects with those set
forth in the Services Agreement.

     c. Conditions to the Sellers’ Obligation to Proceed with Closing. The
obligation of the Sellers to proceed with Closing shall be subject to the
satisfaction or waiver, on or before the Closing Date, of the following:

     I. Representations and Warranties. The representations and warranties set
forth in Section 6 shall be true and correct in all respects at Closing and the
Purchaser shall have complied in all material respects with those covenants
contained in this Agreement that are applicable to it, except in each case as
would not negatively impact the ability of the Purchaser to consummate the
transactions contemplated by this Agreement.

     II. Payment of Share Purchase Price. Purchaser shall be in a position to
pay, simultaneously with the Closing, the Share Purchase Price.

     III. Payment of Bonus Plan Payout Amount. Purchaser shall be in a position
to pay, simultaneously with the Closing, the Bonus Plan Payout Amount.

     IV. Waiver of Non-Competition Covenant. Purchaser shall have delivered to
each officer of the Company who is a party to an employment agreement with the
Company a letter waiving such officer’s compliance with the non-competition
covenant set forth in such agreement; provided, however, that the compliance by
Mitchell L. Solich of the non-solicitation covenant set forth in his employment
agreement shall not be so waived.

     11. Actions to be Taken At Closing.

     a. Sellers’ Actions at Closing. At the Closing, each Seller shall execute,
acknowledge and (upon payment of the funds specified in Section 11(b)(I) and
Section 11(b)(II)) deliver to the Purchaser the following:

     I. Transfer of Shares. The original stock certificates representing such
Seller’s Shares, duly endorsed for transfer (or accompanied by duly executed
stock transfer powers separate from the certificate);

     II. Certificate. A certificate, as to such Seller, certifying that (1) the
representation and warranty set forth in Section 4(d) as to such Seller is true
and correct in all respects as of the Closing Date, (2) the Ownership
Representations (other than the representation and warranty set forth in Section
4(d) as to such Seller) are true and correct in all respects as of the Closing
Date, (3) the representation and warranty set forth in Section 5(v) is true and
correct in all respects as of the Closing Date, (4) the Non-Ownership
Representations (in the

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case of the representations and warranties set forth in Section 4(a),
Section 4(b), Section 4(c) and Section 4(e), as to such Seller) are true and
correct in all respects as of the Closing Date, except to the extent that the
circumstances causing the Non-Ownership Representations not to be true and
correct in all respects would not, individually or in the aggregate, constitute
a Material Adverse Change, and (5) such Seller has complied with the covenants
to which it is subject under this Agreement in all material respects.

     III. Other Necessary Instruments. All other instruments as may be
reasonably required to consummate the agreements of the Parties hereunder.

     b. Purchaser’s Actions at Closing. At Closing, upon the tendering of all of
the Shares, Purchaser shall:

     I. Payment of the Share Purchase Price. Pay to the Sellers, by wire
transfer of immediately available funds, the Share Purchase Price;

     II. Payment of the Bonus Plan Payout Amount. Pay to the Company’s third
party payroll provider, by wire transfer of immediately available funds, the
Bonus Plan Payout Amount to enable such provider to pay to each participant in
the Bonus Pool who has delivered a waiver and release pursuant to Section
10(b)(VII) the portion of the total Bonus Pool Payout Amount to which such
participant is entitled; and

     III. Certificate. Deliver a certificate certifying that the representations
and warranties provided hereunder by the Purchaser are accurate and true in all
material respects as of the Closing and that the Purchaser has complied with the
covenants to which it is subject under this Agreement in all material respects,
except in each case as would not negatively impact the ability of the Purchaser
to consummate the transactions contemplated by this Agreement.

     IV. Payment of Financial Advisors. Pay to Petrie Parkman & Co. and
Rivington Capital Advisors, LLC, by wire transfer of immediately available
funds, the amounts to which such firms are entitled in connection with the
consummation of the transactions contemplated by this Agreement pursuant to
their engagement letters with the Company dated April 7, 2005.

     12. Expiration of Representations, Warranties and Covenants. Except for the
Ownership Representations and the representations made by the Purchaser in
Section 6, which shall survive indefinitely, the representations and warranties
of the Sellers contained herein, and any certificate delivered hereunder, to the
extent that such certificate relates to such representations and warranties,
shall expire at Closing. All covenants and other agreements contained herein
shall survive indefinitely, except for the following: (1) Section 7 shall expire
at Closing, except for Section 7(a) and Section 7(g), both of which shall
survive indefinitely, (2) Section 8 shall expire on the two-year anniversary of
the Closing Date, (3) Section 9 shall expire at Closing, except for the fourth
sentence thereof (solely as it relates to the Sellers’ obligation to cause the
Company to comply with Section 8) and the fifth sentence thereof, both of which
shall

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expire on the two-year anniversary of the Closing Date, (4) Section 10 shall
expire at Closing, and (5) any certificates delivered pursuant to
Section 11(a)(II) (but only to the extent such certificates relate to the
Ownership Representations and the Surviving Covenants) shall expire on the
two-year anniversary of the Closing Date (the covenants and other agreements
which shall survive the Closing being referred to as the “Surviving Covenants”).

     13. Indemnification.

     a. Indemnification. Each Seller severally but not jointly covenants and
agrees that it will indemnify, defend and hold harmless the Purchaser, the
Company and their respective officers, directors, employees, agents,
representatives and affiliates (collectively, the “Purchaser Indemnified
Parties”) from and against all claims, damages, actions, suits, proceedings,
demands, assessments, adjustments, losses, liabilities, diminutions of value,
costs and expenses (including, without limitation, reasonable attorneys’ fees)
(collectively, “Losses”) arising directly or indirectly from, as a result of or
in connection with any breach of the Ownership Representations and the Surviving
Covenants. In respect of the indemnification obligation set forth in the
immediately preceding sentence, (1) no Seller shall be liable for any other
Seller’s breach of Section 4(d), Section 11(a)(I) or the certificate delivered
by any other Seller pursuant to Section 11(a)(II) or for fraud committed by any
other Seller, (2) the liability of each Seller for all claims hereunder shall be
limited in amount to the amount labeled “Distribution Amount” on Exhibit “B” for
each Seller (subject to adjustment pursuant to Section 3) and (3) (A) each
Seller shall be solely liable for such Seller’s breach of Section 4(d),
Section 11(a)(I) or the certificate delivered by such Seller pursuant to
Section 11(a)(II) (to the extent that such certificate relates to such Seller’s
compliance with Section 4(d) and Section 11(a)(I)) or for fraud committed by
such Seller and (B) any Seller’s liability for breaches of any of the Ownership
Representations (other than Section 4(d)) or for breaches of the Surviving
Covenants shall be limited to all Losses resulting from such breach multiplied
by such Seller’s Sharing Ratio. Any claim for indemnification pursuant to this
Section 13(a) based on the breach of a covenant that survives the Closing for a
finite period must be asserted by the Purchaser or a Purchaser Indemnified Party
on or before the expiration of such finite period for such claim to be
enforceable.

     b. Exclusive Remedy for Breaches of Representations, Warranties and
Covenants. Except as specifically set forth in Section 13(a) and the rights of
the Purchaser pursuant to any instrument delivered pursuant to Section 10(b)
(except for the certificates described in Section 10(b)(V)), effective upon the
Closing of the transactions contemplated by this Agreement, in the absence of
fraud on the part of a Seller in connection with the negotiation, execution or
delivery of this Agreement or the consummation of the transactions contemplated
hereby (to the extent determined by a final judgment of a court of competent
jurisdiction), the Purchaser, on behalf of itself and the Purchaser Indemnified
Parties, waives any rights and/or claims it or any other Purchaser Indemnified
Party may have against any Seller, whether in law or equity (except as relates
to adjustments to the Aggregate Purchase Price in accordance with

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Section 3) for any Seller’s breach of a representation or warranty contained in
this Agreement and for breaches of any covenant or other agreement, including,
without limitation, claims for contribution or other rights of recovery arising
out of or relating to any Environmental Laws, claims for breach of contract,
breach of implied covenants, negligent misrepresentation and all other claims
for breach of duty. For the avoidance of doubt, Section 13(a) sets forth the
exclusive remedies available to the Purchaser or the Purchaser Indemnified
Parties for any breach by the Sellers of this Agreement.

     c. NOTHING RELATING TO (1) THE EXPIRATION OF ANY REPRESENTATION, WARRANTY,
COVENANT OR AGREEMENT SET FORTH IN THIS AGREEMENT, (2) THE INDEMNIFICATION
PROVISIONS SET FORTH IN THIS AGREEMENT, (3) THE EXCLUSIVENESS OF ANY REMEDIES
UNDER THIS AGREEMENT OR (4) ANY OTHER MATTER SHALL BE DEEMED TO BE A WAIVER OF
ANY RIGHT OR CLAIM THAT ANY PARTY MAY HAVE AGAINST ANY OTHER PARTY IN RESPECT OF
SUCH PARTY’S FRAUD.

     d. Breaches of MBOW Four Star Corporation Representation. Before seeking
indemnification pursuant to Section 13(a) for a breach by any Seller of the
representations set forth in Section 5(e), the Purchaser shall first pursue any
valid claim for indemnification from Chevron Corp. or its controlled affiliates
relating to the subject matter of such breach.

     14. Termination of Agreement. This Agreement may be terminated as provided
below:

     a. by mutual written consent of the Purchaser and the Majority of Sellers
at any time prior to the Closing;

     b. by the Purchaser if the Closing shall not have occurred on or before
September 30, 2005 for any reason not primarily attributable to the breach by
the Purchaser of any representations, warranties or covenants contained in this
Agreement;

     c. by the Purchaser if the Sellers have breached an Ownership
Representation or the representation in Section 5(v) in any respect, the
Purchaser has notified the Sellers of the breach, and the breach has continued
without cure for a period of 10 business days after the notice of breach;

     d. by the Purchaser if the Sellers have breached a Non-Ownership
Representation or any covenant in this Agreement in any respect and the breach
has continued without cure for a period of 10 business days after the notice of
breach, except to the extent that the breach of any Non-Ownership Representation
or covenant (disregarding all qualifications contained therein regarding
materiality) would not, individually or in the aggregate, constitute a Material
Adverse Change;

     e. by the Purchaser if the Net Defect Amount that is uncured as of the
Closing Date exceeds $80,000,000.00;

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     f. by the Majority of Sellers if the Closing shall not have occurred on or
before September 30, 2005 for any reason not primarily attributable to the
breach by the Sellers or the Company of any representations, warranties or
covenants contained in this Agreement;

     g. by the Majority of Sellers if the Purchaser has breached any
representation, warranty, or covenant contained in this Agreement in any
material respect, the Sellers have notified the Purchaser of the breach, and the
breach has continued without cure for a period of 10 business days after the
notice of breach; or

     h. by the Majority of Sellers if the Net Defect Amount that is uncured as
of the Closing Date exceeds $80,000,000.00.

If this Agreement is terminated (1) by mutual written consent of the Purchaser
and the Majority of Sellers pursuant to Section 14(a), (2) by the Purchaser
pursuant to Section 14(e) or (3) by the Majority of Sellers pursuant to
Section 14(h), then all rights and obligations of the Parties hereunder shall
terminate without any liability of any Party to any other Party. Termination
pursuant to Section 14(b), Section 14(c), Section 14(d), Section 14(f) or
Section 14(g) shall not relieve any Party from any liability for a willful and
material breach by such Party of its covenants and agreements set forth in this
Agreement, and all rights and remedies at law or in equity of the non-breaching
Party in respect of such breach shall be preserved.

     15. General Provisions.

     a. Entire Agreement. This Agreement together with the Schedules and
Exhibits contains the entire understanding of the Parties with regard to the
subject matter hereof and no warranties, representations, promises or agreements
have been made between the Parties other than as expressly herein set forth.
This Agreement supersedes any previous agreement or understanding between the
Parties and cannot be modified or amended except in a writing executed by the
Purchaser and the Majority of Sellers.

     b. Binding Effect. Upon execution, this Agreement shall be binding and
fully enforceable and shall inure to the benefit of the Parties hereto, their
successors, assigns, personal representatives and heirs.

     c. Notices. All notices as may be required by this Agreement shall be
deemed given if delivered personally or sent by facsimile during normal business
hours of the recipient, the next business day if sent by overnight courier, or
upon receipt if sent by U.S. Mail to the respective parties at the addresses set
forth below:

     To Sellers: See Exhibit “A”

     To Purchaser: El Paso Production Holding Company

1001 Louisiana Street
Houston, Texas 77002
Fax: (713) 420-6472
ATTN: Thomas M. Hart III

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With a copies to:

El Paso Production Holding Company
1001 Louisiana Street
Houston, Texas 77002
Fax: (713) 420-6475
ATTN: Eric L. Harry

Andrews Kurth LLP
600 Travis, Suite 4200
Houston, Texas 77002
Fax: (713) 220-4285
ATTN: John B. Clutterbuck
            Peter C. Bowden

     To Company: Medicine Bow Energy Corporation

1225 17th Street, Suite 1900
Denver, Colorado 80202
Fax: (303) 298-5377
ATTN: Mitchell L. Solich

     d. Severability. In the event that any of the provisions, or portions
thereof, of this Agreement are held to be unenforceable or invalid by any court
of competent jurisdiction, the validity and enforceability of the remaining
provisions, or portions thereof, shall not be affected thereby and effect shall
be given to the intent manifested by the provisions, or portions thereof, held
to be enforceable and valid.

     e. Governing Law; Waiver of Jury Trial. This Agreement shall be governed by
and construed under the laws of the State of Delaware without regard to its
choice of law provisions that would apply the law of any other state. EACH OF
THE PARTIES TO THIS AGREEMENT HEREBY IRREVOCABLY WAIVES ALL RIGHT TO A TRIAL BY
JURY IN ANY ACTION, PROCEEDING OR COUNTERCLAIM ARISING OUT OF OR RELATING TO
THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY.

     f. Arbitration of Net Defect Amount Disputes. After Closing, disputed Title
Defects, Title Benefits and Environmental Defects, any disputes relating to the
Net Defect Amount and any disputes as to whether any Title Defect or
Environmental Defect has been cured (collectively, “Arbitrable Disputes”) shall
be submitted to binding arbitration conducted in accordance with the Commercial
Arbitration Rules of the American Arbitration Association (the “AAA”), as
supplemented to the extent necessary to determine any procedural appeal
questions arising under the Federal Arbitration Act (Title 9 of the United
States Code). If there is any inconsistency between this Section 15(f) and the
Commercial Arbitration Rules or the Federal Arbitration Act, then this
Section 15(f) shall control. Arbitration shall be initiated by the Claimant (as
defined below) serving written notice on the Respondent (as defined below) that
the Claimant

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elects to refer the Arbitrable Dispute to binding arbitration. Unless otherwise
agreed by the Parties, a panel of three neutral arbitrators will decide the
Arbitrable Dispute. The Parties shall select the arbitrators as follows: (1) the
Party commencing the arbitration proceeding (the “Claimant”) shall select one
arbitrator and shall notify the other Party (the “Respondent”) in writing of its
selection at the time the Claimant commences the arbitration proceeding; (2) the
Respondent shall select one arbitrator and, within 30 days after receipt of the
Claimant’s designation of arbitrator, shall notify the Claimant in writing of
its selection; (3) if the Respondent fails or refuses to designate an arbitrator
within such period, the Claimant may request the administrator of the Houston
office of the AAA to provide the Parties with a list of potential arbitrators in
accordance with, and the second arbitrator shall be determined pursuant to,
Article 7 of the Commercial Arbitration Rules of AAA; (4) The two arbitrators so
chosen shall select a third arbitrator within 30 days after appointment of the
second arbitrator; and (5) if the Party-appointed arbitrators cannot reach
agreement upon the third arbitrator within the 30-day period, the administrator
of the Houston office of the AAA shall provide the Parties with a list of
potential arbitrators in accordance with, and the third arbitrator shall be
determined pursuant to, Article 7 of the Commercial Arbitration Rules of AAA.
All arbitrators must (1) be neutral persons who have never been officers,
directors, employees, or consultants or had other business relationships with
the Parties or any of their Affiliates, officers, directors or employees, and
(2) have not less than fifteen (15) years recent experience in the U.S. oil and
gas industry relevant to the matters in dispute. The arbitration hearing will be
conducted in Houston, Texas, and shall commence as soon as practicable after the
selection of the third arbitrator. The Parties and the arbitrators shall proceed
diligently and in good faith so that the arbitrators’ determination can be made
as promptly as possible. The arbitrators may consult with and engage
disinterested third parties to advise the arbitrators, including, without
limitation, petroleum engineers, petroleum landmen, and environmental engineers
and consultants, as appropriate. The arbitrators’ determination shall be made in
writing, including findings of fact and conclusions of law, within 45 days after
submission of the matters in dispute. Judgment may be entered on the award, and
the award may be judicially enforced. Except as provided in the Federal
Arbitration Act, the decision of the arbitrators shall be binding on and
non-appealable by the Parties. The arbitrators shall act for the limited purpose
of resolving the specific disputed Title Defects, Title Benefits and
Environmental Defects, any disputes relating to the Net Defect Amount and any
disputes as to whether any Title Defect or Environmental Defect has been cured
and may not award damages, interest or penalties with respect to any matter.
Further, the arbitrators shall have no right or authority to grant or award
indirect, consequential, punitive or exemplary damages of any kind. The Parties
shall each bear their own legal fees and other costs of presenting their case.
The Sellers, on the one hand, and the Purchasers, on the other hand, shall each
pay 50% of the fees and expenses of the arbitrators.

     g. Counterparts; Facsimile Signatures. This Agreement may be executed in
any number of counterparts and each such counterpart shall be considered an
original and an enforceable agreement. Facsimile and electronic signatures to
this Agreement shall be valid.

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     h. Notice of Developments. Each Party will give prompt written notice to
the others of any material breach of any of its representations, warranties and
covenants contained herein.

     i. Exclusivity. Prior to the earlier to occur of (1) the Closing and
(2) the termination of this Agreement, Sellers will not (and the Sellers will
not cause or permit the Company or any representatives, advisors, agents or
controlled affiliates of any Seller or the Company to) intentionally solicit,
initiate, or encourage the submission of any proposal or offer from any Person
relating to the acquisition of any of the issued and outstanding capital stock
of the Company, its Subsidiaries or the Four Star Shares or assets of the
Company or its Subsidiaries having a fair market value in excess of
$5,000,000.00 (including any acquisition structured as a merger, consolidation,
share exchange or other business combination or recapitalization).

     j. Post-Closing Covenants. After Closing, if any further action is
necessary to carry out the purposes of this Agreement, each of the Parties will
take such further action as any other Party reasonably may request, all at the
sole cost and expense of the requesting Party. If any Party is contesting or
defending against any action, suit, proceeding, hearing, investigation, charge,
complaint, claim, or demand in connection with any transaction on or prior to
the Closing Date involving the Company, each of the other Parties shall
cooperate with it and its counsel in the defense or contest, all at the sole
cost and expense of the contesting or defending Party.

     k. Press Releases and Public Announcements. No Party shall issue any press
release or make any public announcement relating to the subject matter of this
Agreement prior to the Closing without the prior written approval of the
Purchaser and the Company; provided, however, that any Party may make any public
disclosure it believes in good faith is required by applicable law, or any
listing or trading agreement concerning its publicly-traded securities (in which
case the disclosing Party will use its reasonable best efforts to advise the
other Parties prior to making the disclosure).

     l. No Third Party Beneficiaries. Except as provided in Section 7(b), this
Agreement shall not confer any rights or remedies upon any Person other than the
Parties and their respective successors and permitted assigns.

     m. Expenses. Notwithstanding anything contained herein, all fees, costs,
and expenses for investment advisors, attorneys and accountants retained by the
Company to facilitate the transactions contemplated by this Agreement shall be
paid by the Company. All fees, costs, and expenses incurred by the Purchaser in
connection with the transactions contemplated by this Agreement shall be paid by
the Purchaser.

     n. Limitation of Damages; Enforcement of Agreement. There shall be no
liability under this Agreement for consequential, special, punitive or exemplary
damages. The Parties agree that irreparable damage may occur in the event that
any of the provisions of this Agreement were not performed in accordance with
its specific terms. Accordingly, the Parties agree that each Party may be
entitled to an injunction or injunctions to prevent breaches of this Agreement
and to specifically enforce the terms

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and provisions of this Agreement in any appropriate court, the foregoing being
in addition to (and not to the exclusion of) any other remedy to which a Party
may be entitled at law or in equity.

     o. Disclosure Generally. Notwithstanding anything to the contrary contained
in the Disclosure Schedules or in this Agreement, the information and
disclosures contained in any Disclosure Schedule shall be deemed to be disclosed
and incorporated by reference in any other Disclosure Schedule as though fully
set forth in such Disclosure Schedule for which applicability of such
information and disclosure is reasonably apparent on its face. The fact that any
item of information is disclosed in any Disclosure Schedule shall not be
construed to mean that such information is required to be disclosed by this
Agreement. Such information and the dollar thresholds set forth herein shall not
be used as a basis for interpreting the terms “material” or “Material Adverse
Effect” or other similar terms in this Agreement.

     p. Legal Representation. In any dispute arising under or in connection with
this Agreement, without limitation, the Sellers, or any one of them, may retain
the firm of Gibson, Dunn & Crutcher LLP to represent them in such matter, and
the Purchaser hereby irrevocably waives and consents to any such representation
in any such matter.

     16. Definitions.

     a. “AAA” is defined in Section 15(f).

     b. “Accrued Tax Amount” means the amount, if any, of the accrued but unpaid
federal income taxes of the Company and its Subsidiaries as of the Closing Date,
which amount shall be estimated by the Parties in good faith at least two
business days prior to the Closing Date in accordance with the Company’s past
custom and practices and shall be net of any reserves for federal income tax
liabilities (excluding any reserves for deferred Taxes established to reflect
timing differences between book and Tax income) set forth or included in the
Most Recent Financial Statements.

     c. “Affiliated Group” is defined in Section 5(i)(I).

     d. “Aggregate Purchase Price” is defined in Section 2(a).

     e. “Allocated Value” means, with respect to an asset of the Company, its
Subsidiaries or Four Star, the portion of the Aggregate Purchase Price allocated
to such asset as set forth in Exhibit “C”.

     f. “Arbitrable Dispute” is defined in Section 15(f).

     g. “Authorized But Unissued Class 12.5 Common Stock” and “Authorized But
Unissued Class 25 Common Stock” shall have the meanings set forth in the
Company’s 2004 Equity Incentive Plan.

     h. “Benefit Plan(s)” means any Pension Plan, Welfare Plan, bonus, deferred
compensation, incentive compensation, stock ownership, stock purchase, stock
option,

Page 31 of 38

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phantom stock, retirement, vacation, severance, disability, death benefit,
hospitalization, medical, dependent care, cafeteria, employee assistance,
scholarship, employment or other similar agreement, plan, program, arrangement
or understanding (whether or not covered under Section 3(3) of ERISA and whether
or not legally binding) that is sponsored, maintained or contributed to by the
Company or any ERISA Affiliate.

     i. “Bonus Plan Payout Amount” is defined in Section 2(a).

     j. “Bonus Pool” is defined in Section 2(a).

     k. “Chevron Indemnified Defects” is defined in Section 3(e).

     l. “Claimant” is defined in Section 15(f).

     m. “Closing” or “Closing Date” shall have the meaning set forth in
Section 2.

     n. “COBRA” means the provisions of the Code and ERISA pertaining to the
Consolidated Omnibus Budget and Reconciliation Act of 1986 as amended, including
the provisions of Section 4980B of the Code and Sections 601 – 608 of ERISA.

     o. “Code” means the Internal Revenue Code of 1986, as amended.

     p. “Company” means Medicine Bow Energy Corporation.

     q. “Company Employee” means a common law employee of the Company or any
ERISA Affiliate.

     r. “Credit Facility” means that certain Second Amended and Restated Credit
Agreement dated December 1, 2003, by and among BNP Paribas, U.S. Bank National
Association, Union Bank of California, the Senior Lenders Signatory thereto, and
the Company and its Subsidiaries, including all amendments thereto.

     s. “CSFB Shareholders” is defined on Exhibit “A”.

     t. “Current General and Administrative Budget of the Company” is set forth
in Exhibit “F”.

     u. “Defect Deductible” is defined in Section 3(d).

     v. “Defect Threshold” is defined in Section 3(d).

     w. “Defensible Title” means, as to an asset, such title of the Company, its
Subsidiaries or Four Star, as applicable, that: (1) is deducible of record from
the records of the county in which the property is located, and (A) in the case
of federal leases, from the records of the applicable office of the Bureau of
Lands Management or Minerals Management Service, or (B) in the case of state
leases, from the applicable records of the applicable state land office;
(2) entitles the Company, its Subsidiaries or, in the case of Four Star, the
percentage equity interest of MBOW Four Star Corporation in Four Star, as

Page 32 of 38

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applicable, to receive not less than the “Net Revenue Interest” set forth in
Exhibit “C” as to such asset, without reduction, suspension or termination
throughout the productive life of such asset; (3) obligates the Company, its
Subsidiaries or, in the case of Four Star, the percentage equity interest of
MBOW Four Star Corporation in Four Star multiplied by Four Star’s interest, as
applicable, to bear costs and expenses relating to operations on and the
maintenance and development of such asset in an amount not greater than the
“Working Interest” set forth in Exhibit “C” with respect to such asset, without
increase for the productive life of such asset (unless there is a corresponding
and proportionate increase in Net Revenue Interest with respect to such asset);
and (4) is free and clear of liens and material encumbrances and defects, except
for Permitted Encumbrances.

     x. “De Minimis Defect” is defined in Section 3(d).

     y. “Distribution Amount” is set forth in Exhibit “B”.

     z. “EnCap Shareholders” is defined on Exhibit “A”.

     aa. “Environmental Approvals” means all applicable permits, licenses,
authorizations and approvals required by governmental authorities pursuant to
any Environmental Law.

     bb. “Environmental Defect” means any non-compliance by the Company, its
Subsidiaries or Four Star with Environmental Laws.

     cc. “Environmental Laws” means all applicable federal, state or local laws,
statutes, codes, ordinances, permits, licenses, rules, regulations and common
law in effect as of the date hereof, and any judicial or administrative
interpretation thereof, including any judicial or administrative order, consent
decree or judgment, relating to the environment or to the emission, discharge,
release, threatened release, use, treatment, storage, disposal, transportation
or handling of pollutants, contaminants or industrial, toxic or hazardous
substances, wastes or materials. Environmental Laws include, but are not limited
to: the Comprehensive Environmental Response, Compensation, and Liability Act of
1980, the Resource Conservation and Recovery Act, the Toxic Substances Control
Act, the Clean Water Act, the Clean Air Act, the Federal Water Pollution Control
Act, the Oil Pollution Control Act, the Endangered Species Act, and the Safe
Drinking Water Act, as such acts may have been amended or supplemented from time
to time, the state and local counterparts or equivalents of all such acts, and
all rules, regulations and orders adopted under any such statutes.

     dd. “ERISA” means the Employee Retirement Income Security Act of 1974, as
amended.

     ee. “ERISA Affiliate” means any corporation or other entity that is
required to be aggregated with the Company or any of its Subsidiaries under
Section 414 (b), (c) or (m) of the Code.

     ff. “Financial Statements” is defined in Section 5(f).

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     gg. “Four Star” is defined in Section 5(e).

     hh. “Four Star Shares” is defined in Section 5(e).

     ii. “Four Star Stockholders Agreement” means that certain Stockholders
Agreement dated as of November 1, 1999, by and between Texaco Inc. (predecessor
to ChevronTexaco Global Energy Inc.), Edison Mission Energy Oil & Gas
(predecessor by way of merger to MBOW Four Star Corporation), Texaco Exploration
and Production Inc. (predecessor to Chevron U.S.A. Inc.), Texaco Nederland B.V.,
Four Star Oil & Gas Holdings (predecessor by way of merger to Four Star Oil &
Gas Company) and Four Star Oil & Gas Company, as further amended, supplemented
or modified from time to time in accordance with the terms thereof.

     jj. “GAAP” means United States generally accepted accounting principles in
effect from time to time.

     kk. “Hedge Obligations” is defined in Section 5(p).

     ll. “Hedge Transactions” is defined in Section 5(p).

     mm. “HSR Act” is defined in Section 7(c).

     nn. “IRS” means the Internal Revenue Service.

     oo. “Kayne Anderson Shareholder” is defined on Exhibit “A”.

     pp. “Liberty Shareholder” is defined on Exhibit “A”.

     qq. “Losses” is defined in Section 13(a).

     rr. “Majority of Sellers” means Sellers representing greater than fifty
percent (50%) of the Shares provided that the Majority of the Seller shall
include the EnCap Shareholders and the CSFB Shareholders.

     ss. “Material Adverse Change” means any actions, suits, arbitrations,
proceedings, facts, circumstances, events, conditions or developments that,
individually or in the aggregate, have had or would be reasonably likely to have
a Material Adverse Effect.

     tt. “Material Adverse Effect” means any material adverse effect on the
business, operations, assets, financial condition or business prospects of the
Company and its Subsidiaries, taken as a whole, except for any such effects
resulting from changes affecting the United States economy, financial and
capital markets or the oil and gas industry in general, or changes in the prices
generally paid for oil, natural gas or equivalents; provided, however, that no
circumstances arising as a result of the announcement or consummation of the
transactions contemplated by this Agreement shall constitute a Material Adverse
Effect.

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     uu. “Most Recent Financial Statements” is defined in Section 5(f).

     vv. “Most Recent Period End” is defined in Section 5(f).

     ww. “Material Agreements” shall have the meaning set forth in Section 5(j).

     xx. “Net Defect Amount” is defined in Section 3(c).

     yy. “Net Revenue Interest” is set forth in Exhibit “C”.

     zz. “Non-Ownership Representations” is defined in Section 10(b).

     aaa. “Objection Deadline” is defined in Section 3(a).

     bbb. “Operating Interests” is defined in Section 5(q).

     ccc. “Ownership Representations” is defined in Section 10(b)(I).

     ddd. “Party” and “Parties” shall mean the Purchaser, the Company and each
Seller.

      eee. “Pension Plan(s)” means any “employee pension benefit plan as such
term is defined in Section 3(2) of ERISA.

      fff. “Permitted Encumbrances” means, with respect to any asset, any and
all of the following: (1) royalties, overriding royalties, production payments,
reversionary interests, convertible interests, net profits interests and similar
burdens encumbering an asset, to the extent the net cumulative effect of such
burdens does not operate to reduce the Company’s or its Subsidiaries’ Net
Revenue Interest in such asset, or, in the case of Four Star, Four Star’s Net
Revenue Interest in such asset multiplied by the percentage equity interest of
MBOW Four Star Corporation in Four Star, to less than that set forth in Exhibit
“C” or increase the Company’s or its Subsidiaries’ Working Interest in such
asset, or, in the case of Four Star, Four Star’s Working Interest in such asset
multiplied by the percentage equity interest of MBOW Four Star Corporation in
Four Star, above that set forth in Exhibit “C” without a corresponding and
proportionate increase in the associated Net Revenue Interest; (2) consents to
assignment and similar contractual provisions affecting transfer of the asset,
provided that such consents, if applicable, have been obtained prior to Closing;
(3) preferential rights to purchase and similar contractual provisions affecting
the asset, provided that such preferential rights, if applicable, have expired
or been waived prior to Closing; (4) rights reserved to or vested in a
governmental entity having jurisdiction to control or regulate the asset, and
all applicable laws of such governmental entities or authorities; (5) easements,
rights-of-way, servitudes, sub-surface leases, equipment, pipelines, and utility
lines on, over and through the asset, provided that they do not materially
interfere with the operation of the asset in the manner such operations were
conducted as of the Closing; (6) terms and conditions of unitization,
communitization, and pooling agreements, and any other similar agreements
affecting the asset, provided that they do not (A) reduce the Company’s or its
Subsidiaries’ Net Revenue Interest in the asset, or, in the case of Four Star,
Four Star’s

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Net Revenue Interest in the asset multiplied by multiplied by the percentage
equity interest of MBOW Four Star Corporation in Four Star, to less than that
set forth on Exhibit “C” or increase the Company’s or its Subsidiaries’ Working
Interest in the asset, or, in the case of Four Star, Four Star’s Working
Interest in the asset multiplied by the percentage equity interest of MBOW Four
Star Corporation in Four Star above that set forth on Exhibit “C” (unless there
is a corresponding and proportionate increase in the associated Net Revenue
Interest), or (B) materially interfere with the operation of the properties of
the Company, its Subsidiaries or Four Star in the manner such operations were
conducted as of Closing; (7) terms and conditions of governmental licenses and
permits affecting the asset; (8) liens for taxes or assessments not yet
delinquent or, if delinquent, being contested in good faith in the ordinary
course of business; (9) liens of operators relating to obligations not yet
delinquent or, if delinquent, being contested in good faith in the ordinary
course of business; (10) mortgages, deeds of trust, liens, pledges, encumbrances
and security interests arising under the Credit Facility; (11) any alleged Title
Defects that have been waived by the Purchaser in writing or not asserted on or
before the expiration of the Objection Period; and (12) such defects or
irregularities in the title to the asset that do not materially interfere with
the ownership, operation, value or use of the asset affected thereby and that
would not be considered material when applying general standards in the oil and
gas industry.

     ggg. “Person” means any individual, corporation, partnership, limited
liability company, joint venture, association, joint-stock company, trust,
enterprise, unincorporated organization, or governmental entity.

     hhh. “Phase I Environmental Inspection” means an assessment of the
Company’s compliance with Environmental Laws consisting of examination of the
Company’s files and public documents, interviews of personnel of the Company and
of other appropriate persons, visual inspection of Company property, and NORM
and asbestos surveys.

     iii. “Purchaser Indemnified Parties” is defined in Section 13.

     jjj. “Records” is defined in Section 7(a).

     kkk. “Respondent” is defined in Section 15(f).

     lll. “Services Agreement” is defined in Section 10(b)(XV).

     mmm. “Share Purchase Price” is defined in Section 2(a).

     nnn. “Shares” shall have the meaning set forth in Paragraph A.

     ooo. “Sharing Ratio” shall be as set forth in Exhibit “B”.

     ppp. “Subscription Agreement” means that certain Subscription Agreement
dated as of December 3, 2003, by and between the Company and the EnCap
Shareholders, the CSFB Shareholders, the Liberty Shareholder and the Kayne
Anderson Shareholder.

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     qqq. “Subsidiary” or “Subsidiaries” means Medicine Bow Operating Company
and MBOW Four Star Corporation. The terms “Subsidiary” and “Subsidiaries” do no
include Four Star.

     rrr. “Surviving Covenants” is defined in Section 12(a).

     sss. “Tax” or “Taxes” means any and all taxes, including any interest,
penalties or other additions to tax that may become payable in respect thereof,
imposed by any federal, state, local or foreign government or any agency or
political subdivision of any such government, which taxes shall include, without
limiting the generality of the foregoing, all income or profits taxes, payroll
and employee withholding taxes, unemployment insurance taxes, social security
taxes, severance taxes, license charges, taxes on stock, sales and use taxes, ad
valorem taxes, excise taxes, franchise taxes, gross receipts taxes, business
license taxes, occupation taxes, real and personal property taxes, stamp taxes,
environmental taxes, transfer taxes, workers’ compensation and other obligations
of the same or of a similar nature to any of the foregoing.

     ttt. “Tax Return” means any report, return (including any information
return), declaration, statement, bill, schedule, claim for refund or written
information required to be supplied to a federal, state, local or foreign taxing
authority in connection with Taxes, including any amendments thereof or any
schedule or attachment thereto.

     uuu. “Title Benefit” means an (1) increase in the Company’s or its
Subsidiaries’ Net Revenue Interest in a property, or, in the case of Four Star,
Four Star’s Net Revenue Interest in a property multiplied by the percentage
equity interest of MBOW Four Star Corporation in Four Star, above that set forth
in Exhibit “C” without a greater than proportionate increase in the Working
Interest above that shown in Exhibit “C” or (2) a decrease in the Company’s or
its Subsidiaries’ Working Interest in a property, or, in the case of Four Star,
Four Star’s Working Interest in a property multiplied by the percentage equity
interest of MBOW Four Star Corporation in Four Star, below that set forth in
Exhibit “C” without a decrease in the Net Revenue Interest for such property
below that shown in Exhibit “C”, which, in each case, increases the value of the
interest of the Company, its Subsidiaries or Four Star, as applicable, in the
affected property by more than $25,000.

     vvv. “Title Defect” means any lien, encumbrance or encroachment on,
irregularity or defect in or objection to title to an asset, other than a
Permitted Encumbrance, that alone or in combination with other Title Defects
causes title to such asset to be less than Defensible Title.

     www. “Warrant” is defined in Section 5(c).

     xxx. “Welfare Plan(s)” means any employee pension benefit plan” as such
term is defined in Section 3(2) of ERISA.

     yyy. “Wells” means all oil and gas wells operated by the Company and its
Subsidiaries or Four Star.

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     zzz. “Working Interest” is set forth in Exhibit “C”.

[SIGNATURES ON NEXT PAGE]

Page 38 of 38

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PURCHASER:

EL PASO PRODUCTION HOLDING COMPANY

         
By:
  /s/ Thomas M. Hart III    
 
       
Name:
  Thomas M. Hart III    
Title:
  Vice President    
Date:
  July 18, 2005    

 

--------------------------------------------------------------------------------

 

COMPANY:

MEDICINE BOW ENERGY CORPORATION

         
By:
  /s/ Mitchell L. Solich    
 
       
Name:
  Mitchell L. Solich    
Title:
  President & Chief Executive Officer    
Date:
  July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

ENCAP ENERGY CAPITAL FUND IV, L.P.

                      By:   EnCap Equity Fund IV GP, L.P., General Partner  
 
                        By:   EnCap Investments L.P., General Partner of EnCap
Equity Fund IV GP, L.P.
 
                            By:   EnCap Investments GP, L.L.C., General Partner
of EnCap             Investments L.P.
 
                   
 
          By:   /s/ D. Martin Phillips    
 
                   
 
          Name:   D. Martin Phillips,    
 
          Title:   Senior Managing Director    
 
          Date:   July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

ENCAP ENERGY CAPITAL FUND IV-B, L.P.

                      By:   EnCap Equity Fund IV GP, L.P., General Partner  
 
                        By:   EnCap Investments L.P., General Partner of EnCap
Equity Fund IV GP, L.P.
 
                            By:   EnCap Investments GP, L.L.C., General Partner
of EnCap Investments L.P.
 
                   
 
          By:   /s/ D. Martin Phillips    
 
                   
 
          Name:   D. Martin Phillips,    
 
          Title:   Senior Managing Director    
 
          Date:   July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

DLJ MERCHANT BANKING PARTNERS III, L.P.

              By:   DLJ Merchant Banking III, Inc., its Managing General Partner
 
 
           
 
  By:   /s/ Kenneth J. Lohsen    
 
           
 
  Name:   Kenneth J. Lohsen    
 
  Title:   Vice President    
 
  Date:   July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

DLJ MERCHANT BANKING III, INC. (AS ADVISORY GENERAL PARTNER ON BEHALF OF DLJ
OFFSHORE PARTNERS III-2, C.V. AND AS ATTORNEY-IN-FACT FOR DLJ MERCHANT BANKING
III, L.P., AS ASSOCIATE GENERAL PARTNER OF DLJ OFFSHORE PARTNERS III-2, C.V.)

         
By:
  /s/ Kenneth J. Lohsen    
 
       
Name:
  Kenneth J. Lohsen    
Title:
  Vice President    
Date:
  July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

DLJ MERCHANT BANKING III, INC. (AS ADVISORY GENERAL PARTNER ON BEHALF OF DLJ
OFFSHORE PARTNERS III-1, C.V. AND AS ATTORNEY-IN-FACT FOR DLJ MERCHANT BANKING
III, L.P., AS ASSOCIATE GENERAL PARTNER OF DLJ OFFSHORE PARTNERS III-1, C.V.)

         
By:
  /s/ Kenneth J. Lohsen    
 
       
Name:
  Kenneth J. Lohsen    
Title:
  Vice President    
Date:
  July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

DLJ OFFSHORE PARTNERS III, C.V.

          By:   DLJ Merchant Banking III, Inc., its Advisory General Partner  
 
       
By:
  /s/ Kenneth J. Lohsen    
 
       
Name:
  Kenneth J. Lohsen    
Title:
  Vice President    
Date:
  July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

DLJ MB PARTNERS III GMBH & CO. KG

                  By:   DLJ Merchant Banking III, L.P., its Managing Limited
Partner    
 
                    By:   DLJ Merchant Banking III, Inc., its General Partner  
 
 
               
 
      By:   /s/ Kenneth J. Lohsen    
 
               
 
      Name:   Kenneth J. Lohsen    
 
      Title:   Vice President    
 
      Date:   July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

MILLENNIUM PARTNERS II, L.P.

              By:   DLJ Merchant Banking III, Inc., its Managing General Partner
 
 
           
 
  By:   /s/ Kenneth J. Lohsen    
 
           
 
  Name:   Kenneth J. Lohsen    
 
  Title:   Vice President    
 
  Date:   July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

MBP III PLAN INVESTORS, L.P.

              By:   DLJ LBO Plans Management Corporation II, its General Partner
 
 
           
 
  By:   /s/ Kenneth J. Lohsen    
 
           
 
  Name:   Kenneth J. Lohsen    
 
  Title:   Vice President    
 
  Date:   July 18, 2005    

 

--------------------------------------------------------------------------------

 

SELLER:

KELLEN HOLDINGS, LLC

         
By:
  /s/ Gregory S. Morzano    
 
       
Name:
  Gregory S. Morzano    
Title:
  Vice President    
Date:
  July 18, 2005    

 

--------------------------------------------------------------------------------

 

            SELLER:

MORRISON ENTERPRISES
      By:     /s/ Kenneth Morrison       Name:     Kenneth Morrison    Title:  
Date:    Business Manager
July 18, 2005   

 

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              SELLER:
 
            KAYNE ANDERSON ENERGY FUND II, L.P.
 
            By:   Kayne Anderson Capital Advisors, L.P., its General Partner
 
                By:   Kayne Anderson Investment Management, Inc., its General
Partner
 
           
 
      By:   /s/ Daniel M. Weingeist
 
           
 
      Name:   Daniel M. Weingeist
 
      Title:   Managing Director
 
      Date:   July 18, 2005

 

--------------------------------------------------------------------------------

 

            SELLER:

GREEN BAY PACKAGING, INC.
      By:     /s/ William F. Kress       Name:     William F. Kress    Title:  
Date:    President & Chief Executive Officer
July 18, 2005   

 

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            SELLER:

MITCHELL L. SOLICH
      /s/ Mitchell L. Solich       Date: July 18, 2005         

 

--------------------------------------------------------------------------------

 

         

            SELLER:

CHRISTOPHER R. WAGNER
      /s/ Christopher R. Wagner       Date: July 18, 2005         

 

--------------------------------------------------------------------------------

 

         

            SELLER:

GEOFF C. SOLICH
      /s/ Geoff C. Solich       Date: July 18, 2005         

 

--------------------------------------------------------------------------------

 

         

            SELLER:

RAWHIDE LLC
      By:     /s/ Mitchell L. Solich       Name:     Mitchell L. Solich   
Title:  
Date:    Manager
July 18, 2005   

 

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            SELLER:

PONDEROSA ENERGY HOLDINGS, LLC
      By:     /s/ Geoff C. Solich       Name:     Geoff C. Solich    Title:  
Date:    Manager
July 18, 2005   

 

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            SELLER:

ERDOLMAN LLC
      By:     /s/ Roger M. Flahive       Name:     Roger M. Flahive     
Title:  
Date:    Manager
July 18, 2005  

 

--------------------------------------------------------------------------------

 

         

            SELLER:

BUCKEYE VENTURES LLC
      By:     /s/ Joseph M. Brooker       Name:     Joseph M. Brooker     
Title:  
Date:    Manager
July 18, 2005  

 

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            SELLER:

OIL PATCH INVESTMENTS, LLC
      By:     /s/ Dan R. Taylor       Name:     Dan R. Taylor      Title:  
Date:    Manager
July 18, 2005