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                                                                   Exhibit 10.12

                            BASIN EXPLORATION, INC.
                    CHANGE OF CONTROL EMPLOYMENT AGREEMENT


          AGREEMENT by and between BASIN EXPLORATION, INC. a Delaware
corporation (the "Company") and THOMAS J. CORLEY (the "Officer"), dated as of
March 24, 1999.

          The Board of Directors of the Company (the "Board"), has determined
that it is in the best interests of the Company and its stockholders to assure
that the Company will have the continued dedication of the Officer,
notwithstanding the possibility, threat or occurrence of a Change of Control (as
defined below) of the Company.  The Board believes it is imperative to diminish
the inevitable distraction of the Officer by virtue of the personal
uncertainties and risks created by a pending or threatened Change of Control and
to encourage the Officer's full attention and dedication to the Company
currently and in the event of any threatened or pending Change of Control, and
to provide the Officer with compensation and benefits arrangements upon a Change
of Control which ensure that the compensation and benefits expectations of the
Officer will be satisfied and which are competitive with those of other
corporations.  Therefore, in order to accomplish these objectives, the Board has
caused the Company to enter into this Agreement.

          NOW, THEREFORE, IT IS HEREBY AGREED AS FOLLOWS:

          1.   Certain Definitions.
               -------------------

               (a)  The "Effective Date" shall mean the first date during the
Change of Control Period (as defined in Section 1(b)) on which a Change of
Control (as defined in Section 2) occurs. Anything in this Agreement to the
contrary notwithstanding, if a Change of Control occurs and if the Officer's
employment with the Company is terminated prior to the date on which the Change
of Control occurs, and if it is reasonably demonstrated by the Officer that such
termination of employment (i) was at the request of a third party who has taken
steps reasonably calculated to effect a Change of Control or (ii) otherwise
arose in connection with or anticipation of a Change of Control, then for all
purposes of this Agreement the "Effective Date" shall mean the date immediately
prior to the date of such termination of employment. For purposes of this
Agreement, the Committee (as described below) may clarify the date as of which a
Change of Control shall be deemed to have occurred.

               (b)  The "Change of Control Period" shall mean the period
commencing on the date hereof and ending on the third anniversary of the date
hereof; provided, however, that commencing on the date one year after the date
hereof, and on each annual anniversary of such date (such date and each annual
anniversary thereof shall be hereinafter referred to as the "Renewal Date"),
unless previously terminated, the Change of Control Period shall be
automatically extended so as to terminate three years from such Renewal Date,
unless at least 60 days prior to the Renewal Date (and prior to the Effective
Date) the Company shall give notice to the Officer that the Change of Control
Period shall not be so extended.
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          2.   Change of Control. For the purpose of this Agreement, a "Change
               -----------------
of Control" shall mean:

               (a)  Any "person" or "group" (within the meaning of Sections
13(d) and 14(d)(2) of the Securities Exchange Act of 1934, as amended (the "1934
Act")), other than a trustee or other fiduciary holding securities under an
employee benefit plan of the Company or Mr. Michael Smith, is or becomes the
"beneficial owner" (as defined in Rule 13d-3 under the 1934 Act), directly or
indirectly, of more than thirty-three and one-third percent (33-1/3%) of the
then outstanding voting stock of the Company; or

               (b)  Individuals who, as of the date hereof, constitute the Board
(and any new director whose election by the Board or whose nomination for
election by the Company's stockholders was approved by a vote of at least two-
thirds of the directors then still in office who either were directors as of the
date hereof or whose election or nomination for election was previously so
approved) cease for any reason to constitute a majority thereof; or

               (c)  The stockholders of the Company approve a merger or
consolidation of the Company with any other corporation, other than a merger or
consolidation which would result in the voting securities of the Company
outstanding immediately prior thereto continuing to represent (either by
remaining outstanding or by being converted into voting securities of the
surviving entity) at least 51% of the combined voting power of the voting
securities of the Company or such surviving entity outstanding immediately after
such merger or consolidation, or the stockholders approve a plan of complete
liquidation of the Company or an agreement for the sale or disposition by the
Company of all or substantially all of the Company's assets; provided, however,
that if the merger, plan of liquidation or sale of substantially all assets is
not consummated following such stockholder approval and the transaction is
abandoned, then the Change of Control shall be deemed not to have occurred.

          3.   Employment Period. The Company hereby agrees to continue the
               -----------------
Officer in its employ, and the Officer hereby agrees to remain in the employ of
the Company subject to the terms and conditions of this Agreement, for the
period commencing on the Effective Date and ending on the third anniversary of
such date (the "Employment Period").

          4.   Terms of Employment.
               -------------------

               (a)  Position and Duties.
                    -------------------

                    (a)  During the Employment Period, (A) the
          Officer's position (including status, offices, titles and
          reporting requirements), authority, duties and
          responsibilities shall be at least commensurate in all
          material respects with the most significant of those held,
          exercised and assigned at any time during the 120-day period
          immediately preceding the Effective Date and (B) the

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          Officer's services shall be performed at the location where
          the Officer was employed 120 days immediately preceding the
          Effective Date or any office or location less than 30 miles
          from such location.

                    (b)  During the Employment Period, and excluding
          any periods of vacation and sick leave to which the Officer
          is entitled, the Officer agrees to devote reasonable
          attention and time during normal business hours to the
          business and affairs of the Company and, to the extent
          necessary to discharge the responsibilities assigned to the
          Officer hereunder, to use the Officer's reasonable best
          efforts to perform faithfully and efficiently such
          responsibilities. During the Employment Period it shall not
          be a violation of this Agreement for the Officer to (A)
          serve on corporate, civic or charitable boards or
          committees, (B) deliver lectures, fulfill speaking
          engagements or teach at educational institutions and (C)
          manage personal investments, so long as such activities do
          not significantly interfere with the performance of the
          Officer's responsibilities as an employee of the Company in
          accordance with this Agreement. It is expressly understood
          and agreed that to the extent that any such activities have
          been conducted by the Officer prior to the Effective Date,
          the continued conduct of such activities (or the conduct of
          activities similar in nature and scope thereto) subsequent
          to the Effective Date shall not thereafter be deemed to
          interfere with the performance of the Officer's
          responsibilities to the Company.

               (b)  Compensation.
                    ------------

                    (a)  Base Salary. During the Employment Period,
                         -----------
          the Officer shall receive an annual base salary ("Annual
          Base Salary"), which shall be paid at a monthly rate, at
          least equal to 12 times the highest monthly base salary paid
          or payable, including any base salary which has been earned
          but deferred, to the Officer by the Company and its
          affiliated companies in respect of the 12-month period
          immediately preceding the month in which the Effective Date
          occurs. During the Employment Period, the Annual Base Salary
          shall be reviewed no more than 12 months after the last
          salary increase awarded to the Officer prior to the
          Effective Date and thereafter at least annually. Any
          increase in Annual Base Salary shall not serve to limit or
          reduce any other obligation to the Officer under this
          Agreement. Annual Base Salary shall not be reduced after any
          such increase and the term Annual Base Salary as utilized in
          this Agreement shall refer to Annual Base Salary as so
          increased. As used in this Agreement, the term "affiliated
          companies" shall

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          include any company controlled by, controlling or under
          common control with the Company.

                    (b)  Annual Bonus. In addition to Annual Base
                         ------------
          Salary, the Officer shall be awarded, for each fiscal year
          ending during the Employment Period, an annual bonus (the
          "Annual Bonus") in cash at least equal to the average of the
          Officer's bonuses over the last three fiscal years, or such
          lesser number of years as the Officer may have been employed
          by the Company, prior to the Effective Date (annualized in
          the event that the Officer was not employed by the Company
          for an entire fiscal year) (the "Recent Annual Bonus"). Each
          such Annual Bonus shall be paid no later than the end of the
          third month of the fiscal year next following the fiscal
          year for which the Annual Bonus is awarded, unless the
          Officer shall elect to defer the receipt of such Annual
          Bonus.

                    (c)  Incentive, Savings and Retirement Plans.
                         ---------------------------------------
          During the Employment Period, the Officer shall be entitled
          to participate in all incentive, savings and retirement
          plans, practices, policies and programs applicable generally
          to other peer executives of the Company and its affiliated
          companies but in no event shall such plans, practices,
          policies and programs provide the Officer with incentive
          opportunities (measured with respect to both regular and
          special incentive opportunities to the extent, if any, that
          such distinction is applicable), savings opportunities and
          retirement benefit opportunities, in each case, less
          favorable, in the aggregate, than the most favorable of
          those provided by the Company and its affiliated companies
          for the Officer under such plans, practices, policies and
          programs as in effect at any time during the 120-day period
          immediately preceding the Effective Date or if more
          favorable to the Officer, those provided generally at any
          time after the Effective Date to other peer executives of
          the Company and its affiliated companies.

                    (d)  Welfare Benefit Plans. During the Employment
                         ---------------------
          Period, the Officer and/or the Officer's family, as the case
          may be, shall be eligible for participation in and shall
          receive all benefits under welfare benefit plans, practices,
          policies and programs provided by the Company and its
          affiliated companies (including, without limitation,
          medical, prescription, dental, disability, salary
          continuance, employee life, group life, accidental death and
          travel accident insurance plans and programs) to the extent
          applicable generally to other peer executives of the Company

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          and its affiliated companies, but in no event shall such
          plans, practices, policies and programs provide the Officer
          with benefits which are less favorable, in the aggregate,
          than the most favorable of such plans, practices, policies
          and programs in effect for the Officer at any time during
          the 120-day period immediately preceding the Effective Date
          or, if more favorable to the Officer, those provided
          generally at any time after the Effective Date to other peer
          executives of the Company and its affiliated companies.

                    (e)  Expenses. During the Employment Period, the
                         --------
          Officer shall be entitled to receive prompt reimbursement
          for all reasonable expenses incurred by the Officer in
          accordance with the most favorable policies, practices, and
          procedures of the Company and its affiliated companies in
          effect for the Officer at any time during the 120-day period
          immediately preceding the Effective Date or, if more
          favorable to the Officer, as in effect generally at any time
          thereafter with respect to other peer executives of the
          Company and its affiliated companies.

                    (f)  Fringe Benefits. During the Employment
                         ---------------
          Period, the Officer shall be entitled to fringe benefits,
          including, without limitation, in accordance with the most
          favorable plans, practices, programs and policies of the
          Company and its affiliated companies in effect for the
          Officer at any time during the 120-day period immediately
          preceding the Effective Date or, if more favorable to the
          Officer, as in effect generally at any time thereafter with
          respect to other peer executives of the Company and its
          affiliated companies.

                    (g)  Vacation. During the Employment Period, the
                         --------
          Officer shall be entitled to paid vacation in accordance
          with the most favorable plans, policies, programs and
          practices of the Company and its affiliated companies as in
          effect for the Officer at any time during the 120-day period
          immediately preceding the Effective Date or, if more
          favorable to the Officer, as in effect generally at any time
          thereafter with respect to other peer executives of the
          Company and its affiliated companies.

          5.   Termination of Employment.
               -------------------------

               (a)  Death or Disability. The Officer's employment shall
                    -------------------
terminate automatically upon the Officer's death during the Employment Period.
If the Company determines in good faith that the Disability of the Officer has
occurred during the Employment Period (pursuant to the definition of Disability
set forth below), it may give to the Officer written

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notice in accordance with Section 12(b) of this Agreement of its intention to
terminate the Officer's employment. In such event, the Officer's employment with
the Company shall terminate effective on the 30th day after receipt of such
notice by the Officer (the "Disability Effective Date"), provided that, within
the 30 days after such receipt, the Officer shall not have returned to full-time
performance of the Officer's duties. For purposes of this Agreement,
"Disability" shall mean the absence of the Officer from the Officer's duties
with the Company on a full-time basis for 180 consecutive business days as a
result of incapacity due to mental or physical illness which is determined to be
total and permanent by a physician selected by the Company or its insurers and
acceptable to the Officer or the Officer's legal representative.

               (b)  Cause. The Company may terminate the Officer's employment
                    -----
during the Employment Period for Cause. For purposes of this Agreement, "Cause"
shall mean:

                    (a)  the Officer's gross violation of the terms of
          this Agreement, if such violation has not been substantially
          cured within thirty (30) days following written notice to
          the Officer from the Company of such violation setting forth
          with specificity the nature of the violation or, if cure
          cannot reasonably be effected within such 30-day period, if
          the Officer does not commence such cure within such 30-day
          period and thereafter pursue such cure continuously and with
          due diligence until cure has been effected;

                    (b)  the Officer's willful dishonesty towards,
          fraud upon, felony crime against, deliberate material injury
          or material bad faith action with respect to, or deliberate
          or attempted injury to the Company; or

                    (c)  the Officer's conviction for any felony crime
          (whether in connection with the Company's affairs or
          otherwise).

               (c)  Good Reason; Window Period.  The Officer's employment may be
                    --------------------------
terminated (i) during the Employment Period by the Officer for Good Reason or
(ii) during the Window Period by the Officer without any reason.  For purposes
of this Agreement, "Window Period" shall mean the 30-day period immediately
following the Effective Date.  For purposes of this Agreement, any termination
by the Officer during the Window Period shall be deemed a termination by the
Officer for Good Reason and, in addition, "Good Reason" shall mean:

                    (a)  the assignment to the Officer by the Company
          following the Effective Date of any duties inconsistent
          with, or a substantial alteration in the nature or status
          of, the Officer's responsibilities as in effect during the
          120-day period prior to the Effective Date, including a
          change in the Officer's title or the level of supervisor to
          whom the Officer is required to report;

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                    (b)  a failure by the Company to comply with any
          of the provisions of Section 4(b) of this Agreement other
          than an isolated, insubstantial and inadvertent failure not
          occurring in bad faith and which is remedied by the Company
          promptly after receipt of notice thereof given by the
          Officer;

                    (c)  a relocation of the Company's principal
          offices to a location outside a 30-mile radius of Denver,
          Colorado, or the Officer's relocation to any place other
          than the offices of the Company located in Denver, Colorado
          or within 30 miles of Denver, Colorado, except for
          reasonably required travel by the Officer on the Company's
          business to an extent substantially consistent with the
          Officer's business travel obligations immediately preceding
          the Effective Date;

                    (d)  any material breach by the Company of any
          provision of this Agreement, if such material breach has not
          been cured within thirty (30) days following written notice
          by the Officer to the Company of such breach setting forth
          with specificity the nature of the breach;

                    (e)  any failure by the Company to obtain the
          assumption and performance of this Agreement by any
          successor (by merger, consolidation or otherwise) or assign
          of the Company; or

                    (f)  the voluntary termination by Michael S. Smith
          of his employment as Chief Executive Officer of the Company
          or the termination of his employment as Chief Executive
          Officer in the event of a Change of Control; provided that
          such termination shall constitute Good Reason only for a
          period of 120 days from the date of termination of Mr.
          Smith's employment as Chief Executive Officer.

For purposes of this Section 5(c), any good faith determination of "Good Reason"
made by the Officer shall be conclusive.

               (d)  Notice of Termination. Any termination by the Company for
                    ---------------------
Cause, or by the Officer for Good Reason, shall be communicated by Notice of
Termination to the other party hereto given in accordance with Section 12(b) of
this Agreement.  For purposes of this Agreement, a "Notice of Termination" means
a written notice which (i) indicates the specific termination provision in this
Agreement relied upon, (ii) to the extent applicable, sets forth in reasonable
detail the facts and circumstances claimed to provide a basis for termination of
the Officer's employment under the provision so indicated and (iii) if the Date
of Termination (as

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<PAGE>

defined below) is other than the date of receipt of such notice, specifies the
termination date (which date shall be not more than 30 days after the giving of
such notice). The failure by the Officer or the Company to set forth in the
Notice of Termination any fact or circumstance which contributes to a showing of
Good Reason or Cause shall not waive any right of the Officer or the Company,
respectively, hereunder or preclude the Officer or the Company, respectively,
from asserting such fact or circumstance in enforcing the Officer's or the
Company's rights hereunder.

               (e)  Date of Termination.  "Date of Termination" means (i) if the
                    -------------------
Officer's employment is terminated by the Company for Cause, or by the Officer
for Good Reason, the date of receipt of the Notice of Termination or any later
date specified therein, as the case may be, (ii) if the Officer's employment is
terminated by the Company other than for Cause or Disability, the Date of
Termination shall be the date on which the Company notifies the Officer of such
termination, (iii) if the Officer's employment is terminated by reason of
Disability, the Date of Termination shall be the Disability Effective Date, and
(iv) if the Officer's employment is terminated by reason of his death, the Date
of Termination shall be the last day of the month during which his death occurs.

          6.   Obligations of the Company upon Termination.
               -------------------------------------------

               (a)  Good Reason; Other Than for Cause, Death or Disability.  If,
                    ------------------------------------------------------
during the Employment Period, the Company shall terminate the Officer's
employment other than for Cause or Disability or the Officer shall terminate
employment for Good Reason, the parties acknowledge that the Officer will
sustain actual damages, the amount of which is indefinite, uncertain and
difficult of exact ascertainment because of the uncertainties of successfully
relocating and seeking a comparable position.  In order to avoid dispute as to
the amount of such damages and the mutual expense and inconvenience such dispute
would entail, the Company and the Officer have agreed hereby that the Company
shall pay to the Officer compensation as provided below.  It is hereby agreed
that in the event of such termination by the Company, the Officer shall receive
such amounts as herein provided, not as a penalty, but as the Officer's agreed
compensation and sole damages for the termination of this Agreement, in lieu of
the Officer's proof of his actual damages on that account.  If, during the
Employment Period, the Company shall terminate the Officer's employment other
than for Cause or Disability or the Officer shall terminate employment for Good
Reason, the Company shall pay to the Officer in a lump sum in cash within 5 days
after the Date of Termination the aggregate of the following amounts:

                    (a)  the sum of (1) the Officer's Annual Base
          Salary through the Date of Termination to the extent not
          theretofore paid, (2) the product of (x) the higher of (I)
          the Recent Annual Bonus and (II) the Annual Bonus paid or
          payable, including any bonus or portion thereof which has
          been earned but deferred (and annualized for any fiscal year
          consisting of less than 12 full months or during which the
          Officer was employed for less than 12 full months), for the
          most recently completed fiscal year during the Employment
          Period, if any (such higher amount being referred to

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          as the "Highest Annual Bonus") and (y) a fraction, the
          numerator of which is the number of days in the current
          fiscal year through the Date of Termination, and the
          denominator of which is 365 and (3) any compensation
          previously deferred by the Officer (together with any
          accrued interest or earnings thereon) and any accrued
          vacation pay, in each case to the extent not theretofore
          paid (the sum of the amounts described in clauses (1), (2),
          and (3) shall be hereinafter referred to as the "Accrued
          Obligations"); and

                    (b)  the amount equal to the product of (1) three
          and (2) the sum of (x) the Officer's Annual Base Salary and
          (y) the Highest Annual Bonus.

          To the extent not theretofore paid or provided, the Company shall
timely pay or provide to the Officer any other amounts or benefits required to
be paid or provided or which the Officer is eligible to receive under any plan,
program, policy or practice or contract or agreement of the Company and its
affiliated companies (such other amounts and benefits shall be hereinafter
referred to as the "Other Benefits").

          In addition, any options to purchase shares of the Company's common
stock shall immediately vest and become exercisable as of the Date of
Termination and, notwithstanding anything to the contrary in the Officer's
option agreements with the Company, the options shall be exercisable for a
period of 12 months after the Date of Termination (but in no event beyond the
expiration date applicable to such options).  Any restrictions on restricted
stock grants and performance share grants shall also be eliminated.

               (b)  Death. If the Officer's employment is terminated by reason
                    -----
of the Officer's death during the Employment Period, this Agreement shall
terminate without further obligations to the Officer's legal representatives
under this Agreement, other than for payment of Accrued Obligations and the
timely payment or provision of Other Benefits. Accrued Obligations shall be paid
to the Officer's estate or beneficiary, as applicable, in a lump sum in cash
within 5 days of the Date of Termination. With respect to the provision of Other
Benefits, the term Other Benefits as utilized in this Section 6(b) shall
include, without limitation, and the Officer's estate and/or beneficiaries shall
be entitled to receive, benefits at least equal to the most favorable benefits
provided by the Company and affiliated companies to the estates and
beneficiaries of peer executives of the Company and such affiliated companies
under such plans, programs, practices and policies relating to death benefits,
if any, as in effect with respect to other peer executives and their
beneficiaries at any time during the 120-day period immediately preceding the
Effective Date or, if more favorable to the Officer's estate and/or the
Officer's beneficiaries, as in effect on the date of the Officer's death with
respect to other peer executives of the Company and its affiliated companies and
their beneficiaries.

               (c)  Disability. If the Officer's employment is terminated by
                    ----------
reason of the Officer's Disability during the Employment Period, this Agreement
shall terminate without

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further obligations to the Officer, other than for payment of Accrued
Obligations and the timely payment or provision of Other Benefits. Accrued
Obligations shall be paid to the Officer in a lump sum in cash within 5 days of
the Date of Termination. With respect to the provision of Other Benefits, the
term Other Benefits as utilized in this Section 6(c) shall include, and the
Officer shall be entitled after the Disability Effective Date to receive,
disability and other benefits at least equal to the most favorable of those
generally provided by the Company and its affiliated companies to disabled
executives and/or their families in accordance with such plans, programs,
practices and policies relating to disability, if any, as in effect generally
with respect to other peer executives and their families at any time during the
120-day period immediately preceding the Effective Date or, if more favorable to
the Officer and/or the Officer's family, as in effect at any time thereafter
generally with respect to other peer executives of the Company and its
affiliated companies and their families.

               (d)  Cause; Other than for Good Reason. If the Officer's
                    ---------------------------------
employment shall be terminated for Cause during the Employment Period, this
Agreement shall terminate without further obligations to the Officer other than
the obligation to pay to the Officer (x) his Annual Base Salary through the Date
of Termination, (y) the amount of any compensation previously deferred by the
Officer, and (z) Other Benefits, in each case to the extent theretofore unpaid.
If the Officer voluntarily terminates employment during the Employment Period,
excluding a termination for Good Reason, this Agreement shall terminate without
further obligations to the Officer, other than for Accrued Obligations and the
timely payment or provision of Other Benefits. In such case, all Accrued
Obligations shall be paid to the Officer in a lump sum in cash within 5 days of
the Date of Termination.

          7.   Non-exclusivity of Rights.  Except as provided in Sections
               -------------------------
6(a)(ii), 6(b) and 6(c), nothing in this Agreement shall prevent or limit the
Officer's continuing or future participation in any plan, program, policy or
practice provided by the Company or any of its affiliated companies and for
which the Officer may qualify, nor, subject to Section 12(f), shall anything
herein limit or otherwise affect such rights as the Officer may have under any
contract or agreement with the Company or any of its affiliated companies.
Amounts which are vested benefits or which the Officer is otherwise entitled to
receive under any plan, policy, practice or program of or any contract or
agreement with the Company or any of its affiliated companies at or subsequent
to the Date of Termination shall be payable in accordance with such plan,
policy, practice or program or contract or agreement except as explicitly
modified by this Agreement.

          8.   Full Settlement.  The Company's obligation to make the payments
               ---------------
provided for in this Agreement and otherwise to perform its obligations
hereunder shall not be affected by any set-off, counterclaim, recoupment,
defense or other claim, right or action which the Company may have against the
Officer or others.  In no event shall the Officer be obligated to seek other
employment or take any other action by way of mitigation of the amounts payable
to the Officer under any of the provisions of this Agreement and such amounts
shall not be reduced whether or not the Officer obtains other employment.  The
Company agrees to pay as incurred, to the full extent permitted by law, all
legal fees and expenses which the Officer may reasonably incur as a result of
any contest (regardless of the outcome thereof but not in the case of fees
incurred with

                                      -10-
<PAGE>

respect to a claim brought in bad faith) by the Company, the Officer or others
of the validity or enforceability of, or liability under, any provision of this
Agreement or any guarantee of performance thereof (including as a result of any
contest by the Officer about the amount of any payment pursuant to this
Agreement), plus in each case interest on any delayed payment at the applicable
Federal rate provided for in Section 7872(f)(2)(A) of the Internal Revenue Code
of 1986, as amended (the "Code").

          9.   Limitation on Amount of Payment.
               -------------------------------

               (a)  Limitation. Notwithstanding anything else in this Agreement,
                    ----------
solely in the event of a termination by the Company without Cause or a
termination by the Officer for Good Reason, and except as provided in subsection
(i) below, the aggregate of the payments of benefits to which the Officer will
be entitled under Section 6(a) will be reduced to the extent necessary so that
the Officer will not be liable for the federal excise tax levied on certain
"excess parachute payments" under section 4999 of the Internal Revenue Code.

                    (i)  The limitation of Section 9(a) will not apply if the
          difference between (w) the present value of all payments to which the
          Officer is entitled under paragraph 6(a) determined without regard to
          Section 9(a) less (x) the present value of all federal, state and
          other income and excise taxes for which the Officer is liable as a
          result of such payments exceeds the difference between (y) the present
          value of all payments to which the Officer is entitled under Section
          6(a) calculated as if the limitation of Section 9(a) applies less (z)
          the present value of all federal, state and other income and excise
          taxes for which the Officer is liable as a result of such reduced
          payments. Present values will be determined using the interest rate
          specified in section 280G of the Internal Revenue Code and will be the
          present values as of the date on which the Officer's employment
          terminates (unless it is necessary to use a different date in order to
          avoid adverse consequences under section 280G).

          (b)  Determination by Officer. Whether payments to the Officer are to
               ------------------------
be reduced pursuant to Section 9(a), and the extent to which they are to be so
reduced, will be determined by the Officer. The Officer may, at the expense of
the Company, hire an accounting firm, law firm or employment consulting firm
selected by the Officer to assist him in such determination. If a reduction is
made pursuant to Section 9(a), the Officer will have the right to determine
which payments and benefits will be reduced.

          (c)  Additional Benefit. The Officer shall receive the benefit of any
               ------------------
change made by the Company in the calculation or entitlement of severance
compensation following a Change of Control for any other officer of the Company,
such as an agreement by the Company to "gross up" the compensation paid to an
officer by paying the excise tax imposed by Section 280G of the Internal Revenue
Code.

          10.  Confidential Information. The Officer shall not, during his
               ------------------------
employment by the Company or at any time thereafter, directly or indirectly use,
divulge, furnish or make accessible to anyone other than the Company, its
directors or officers (otherwise than in the

                                      -11-
<PAGE>

regular course of the business of the Company), any knowledge or information
regarding any confidential or secret activities, prospects, technical data,
analysis and interpretations, projects, plans, reports, investor or co-venturer
names or lists, financial or marketing information or documentary material
relating to the existing, planned or contemplated business or activities of the
Company. The Officer, upon leaving the employ of the Company, shall not take
with him or retain any books, records, data, reports, letters, memoranda, notes
or other writings or documents whatsoever, or copies thereof, which reflect or
deal with any secret, proprietary or confidential information or material
relating to the business or activities of the Company. The obligations of the
Officer under this Section 10 shall not apply to (i) information which at the
time of disclosure is readily available to the public; (ii) information which is
or becomes available to the general public other than through acts or omissions
attributable to the Officer; or (iii) information obtained from a third party
who is lawfully in possession of the same other than through breach of a
confidentiality or nonuse obligation owed to the Company or others with respect
to that information.

          11.  Successors.
               ----------

               (a)  This Agreement is personal to the Officer and, without the
prior written consent of the Company, shall not be assignable by the Officer
otherwise than by will or the laws of descent and distribution. This Agreement
shall inure to the benefit of and be enforceable by the Officer's legal
representatives.

               (b)  This Agreement shall inure to the benefit of and be binding
upon the Company and its successors and assigns.

               (c)  The Company will require any successor (whether direct or
indirect, by purchase, merger, consolidation or otherwise) to all or
substantially all of the business and/or assets of the Company to assume
expressly and agree to perform this Agreement in the same manner and to the same
extent that the Company would be required to perform it if no such succession
had taken place.  As used in this Agreement, "Company" shall mean the Company as
hereinbefore defined and any successor to its business and/or assets as
aforesaid which assumes and agrees to perform this Agreement by operation of
law, or otherwise.

          12.  Miscellaneous.
               -------------

               (a)  Governing Law. This Agreement shall be governed by and
                    -------------
construed in accordance with the laws of the State of Delaware, without
reference to principles of conflict of laws. The captions of this Agreement are
not part of the provisions hereof and shall have no force or effect. This
Agreement may not be amended or modified otherwise than by a written agreement
executed by the parties hereto or their respective successors and legal
representatives.

                                      -12-
<PAGE>

               (b)  Notices. All notices and other communications hereunder
                    -------
shall be in writing and shall be given by hand delivery to the other party or by
registered or certified mail, return receipt requested, postage prepaid,
addressed as follows:

               If to the Officer:

               Thomas J. Corley
               10092 Hooker Way
               Westminster, Colorado 80030

               If to the Company:

               Basin Exploration, Inc.
               370 Seventeenth Street, Suite 3400
               Denver, Colorado 80002

               Attention:  General Counsel or President

or to such other address as either party shall have furnished to the other in
writing in accordance herewith.  Notice and communications shall be effective
when actually received by the addressee.

               (c)  Severability. The invalidity or unenforceability of any
                    ------------
provision of this Agreement shall not affect the validity or enforceability of
any other provision of this Agreement.

               (d)  Withholdings. The Company may withhold from any amounts
                    ------------
payable under this Agreement the minimum amounts of any such Federal, state,
local or foreign taxes as shall be required to be withheld pursuant to any
applicable law or regulation.

               (e)  Modifications. The Officer's or the Company's failure to
                    -------------
insist upon strict compliance with any provision of this Agreement or the
failure to assert any right the Officer or the Company may have hereunder,
including, without limitation, the right of the Officer to terminate employment
for Good Reason pursuant to Section 5(c)(i)-(v) of this Agreement, shall not be
deemed to be a waiver of such provision or right or any other provision or right
of this Agreement.

               (f)  Acknowledgment of Employment at Will. The Officer and the
                    ------------------------------------
Company acknowledge that, except as may otherwise be provided under any other
written agreement between the Officer and the Company, the employment of the
Officer by the Company is "at will" and, subject to Section 1(a) hereof, prior
to the Effective Date, the Officer's employment and/or this Agreement may be
terminated by either the Officer or the Company at any time prior to the
Effective Date, in which case the Officer shall have no further rights under
this Agreement. From and after the Effective Date, this Agreement shall
supersede any other agreement between the parties with respect to the subject
matter hereof.

                                      -13-
<PAGE>

          IN WITNESS WHEREOF, the Officer has hereunto set the Officer's hand
and, pursuant to the authorization from its Board of Directors, the Company has
caused these presents to be executed in its name on its behalf, all as of the
day and year first above written.

                                /s/ Thomas J. Corley
                                ---------------------------------------
                                Thomas J. Corley



                                BASIN EXPLORATION, INC.



                                By: /s/ Michael S. Smith
                                    -----------------------------------
                                    Michael S. Smith, President

                                      -14-