<PAGE>   1
                                                                   EXHIBIT 10.27

                             ADOPTION AGREEMENT FOR

                              COHO RESOURCES, INC.

                              401(K) SAVINGS PLAN

         This agreement, executed on the _______ day of _______, 199_, by Coho 
Resources, Inc. (Hereinafter referred to as the "Employer"), a Nevada
Corporation, and R. Lynn Guillory, Joseph R. Ragusa and Susan McAden
(hereinafter referred to collectively as the "Trustees").

                               W I T N E S S E T H

         WHEREAS, effective October 15, 1990, the Employer heretofore
established for the exclusive benefit of its eligible employees and their
beneficiaries, a defined contribution plan and trust intended to qualify under
Sections 401(a) and 501(a) of the Internal Revenue Code of 1986, as amended
(hereinafter referred to as the "Code") to recognize the efforts made to its
successful operation by its employees and to reward such contribution; and

         WHEREAS, the Employer has heretofore maintained such plan and trust,
known as the Coho Resources, Inc. 401(k) Savings Plan (which plan and trust are
hereinafter referred to as the "Plan"), in a manner intended to ensure that the
Plan continues to qualify under Sections 401(a) and 501(a) of the Code, as
amended; and

         WHEREAS, the Employer intends to provide that the Plan complies with
provisions of the Tax Reform Act of 1986 (TRA '86), the Omnibus Budget
Reconciliation Acts of 1986, 1987, 1989 and 1993 (OBRA '86, OBRA '87, OBRA '89,
and OBRA '93), the Technical and Miscellaneous Revenue Act of 1988 (TAMRA), the
Unemployment Compensation Amendments Act of 1992 (UCA), the Employee Retirement
Income Security Act of 1974 (ERISA), and the Code, and the regulations
promulgated thereunder; and

         WHEREAS, pursuant to the Plan, the Employer reserved the right at any
time and from time to time to amend the Plan subject to certain terms and
conditions therein set forth; and

         WHEREAS, by reason of the acquisition of Mid Louisiana Gas Company
("MLG") by Coho Energy, Inc., the Board of Directors of the Corporation deem it
desirable to merge the assets and/or liabilities of the MLG Plan with the assets
and/or liabilities of the Plan; and

         WHEREAS, pursuant to a Resolution by the Board of Directors of the
Employer, the Employer has resolved to merge the MLG Plan with the Plan,
effective July 1, 1995; and

         WHEREAS, the Employer desires to amend and restate the Plan effective
July 1, 1995, except where otherwise provided; and

         NOW, THEREFORE, in consideration of the premises and mutual covenants
contained herein, the Employer and the Trustee hereby agree to amend and restate
the Plan in its entirety, effective July 1, 1995, except where otherwise
provided, notwithstanding any other provisions of the Plan to the contrary as
follows:



<PAGE>   2


1. THE EMPLOYER: Coho Resources, Inc.

   A. The Employer's address and telephone number are:

      Coho Resources, Inc,
      14785 Preston Road, Suite 860
      Dallas, Texas 75240
      (214) 991-9493

   B. The Employer's taxpayer identification number:

      84-0824557

   C. The Employer's fiscal year is:

      January 1 - December 31

   D. The Plan Year is the following twelve (12) consecutive-month period:

      January 1 - December 31

   E. The Plan Anniversary Date is:

      December 31

   F. The Plan Administrator is:

      Coho Resources, Inc.
      14785 Preston Road, Suite 860
      Dallas, Texas 75240
      (214) 991-9493

   G. The original Effective Date of the Plan is:

      October 15, 1990.

   H. The Plan is:

      Coho Resources, Inc. 401(k) Savings Plan (as amended and restated in this
      Adoption Agreement and the related basic plan document and subsequent
      amendments thereto).

   I. The Plan Number is:

      001



                                       ii



<PAGE>   3





II.  ELIGIBILITY AND SERVICE:

      A. An Employee shall be eligible to participate in the Plan on the Entry
         Date coincident with or next following; 

         attainment of age twenty one (21).

      B. Service credited to any Employee of Mid Louisiana Gas Company shall be
         counted as service with Coho Resources, Inc. for the purposes of
         determining such Employees' eligibility to participate in the Plan.
         Service shall be determined as of the date an Employee was first
         credited with one (1) hour of service with Mid Louisiana Gas Company.

      C. An Employee of Mid Louisiana Gas Company who is a Participant in the
         MLG Plan on July 1, 1995 shall be eligible to participate in the Plan
         notwithstanding any eligibility requirements.

      D. An Employee of Coho Resources, Inc, who is a Participant in the Plan on
         June 30, 1995, shall be eligible to participate in the Plan
         notwithstanding any eligibility requirements.

      E. Entry Dates shall occur each Plan Year on 

         January 1, April 1, July 1 and October 1

      F. Years of Service shall be determined under the Elapsed Time Method,
         pursuant to Plan Section 1.78(b).

      G. All Years of Service with the Employer shall be credited for purposes
         of eligibility and vesting.

III. CONTRIBUTIONS:

      A. Salary Deposit Contributions:

         1.       For any Plan Year, the amount specified in a Salary Deposit
                  Agreement by a Participant shall be between 0% and 15% of
                  Participant's Plan Year Compensation.

         2.       Salary Deposit Agreements may be changed more frequently than
                  semi-annually if so authorized by the Plan Administrator.

      B. Matching Contributions.

         Matching Contributions may be made by the Employer, at its sole
         discretion, at least annually.

      C. Eligibility for Matching Contributions:

         Participants eligible to receive a Matching Contribution, if any, for a
         Plan Year shall be only those Participants who made a Salary Deposit
         Contribution during the Plan Year.

                                      iii



<PAGE>   4





      D. Maximum Salary Deposit Contributions Matched:

         1.       The amount of the Employer Matching Contribution, if any,
                  shall be between 0% and 100% (to be determined at the
                  Employer's discretion) of the portion of each Participant's
                  Salary Deposit Contribution that qualify for a matching
                  contribution.

         2.       In determining Matching Contributions, Salary Deposit
                  Contributions up to an amount equal to 8% of a Participant's
                  Compensation shall qualify for the Employer Matching
                  Contribution.

      E. Related and Unrelated Rollover Contributions to the Plan (as described
         in Plan Section 1.64) shall be allowed.

      F. Discretionary Contributions shall not be made by the Employer.

      G. Nondeductible Employee Contributions shall not be allowed.

      H. Transfers directly from other plans to this Plan (as described in Plan
         Section 3.13(b)) shall not be allowed.

IV. FORFEITURES:

      A. Forfeitures attributable to Matching Contributions shall be used to
         reduce the Matching Contribution of the Employer in accordance with
         Section 4.06(d)(4)(A) of the Plan.

V. DEFINITIONS OF COMPENSATION:

      A. Code Section 415(c) Compensation shall be defined as set forth in
         Section 1.12(b)(10)(A) of the Plan.

      B. Code section 414(s) Compensation shall:

         1.       mean Compensation as defined in Section 1.12(d)(1) of the
                  Plan, and shall include Salary Deposit Contributions under the
                  Plan and any salary reductions made under a Code Section 125
                  plan; and

         2.       be limited to the period for which an Employee is a
                  Participant in the Plan.

                                       iv



<PAGE>   5


VI. VESTING:

      A. A Participant's Vested Balanced in his/her Employer Matching Account
         shall be determined on the basis of the following Vesting Schedule:

<TABLE>
<CAPTION>
                Years of Service                    Vested Percentage
                ----------------                    -----------------
<S>                                                 <C> 
                        0                                    0%
                        1                                   20%
                        2                                   40%
                        3                                   60%
                        4                                   80%
                5 years or more                            100%
</TABLE>

VII DISTRIBUTIONS AND WITHDRAWALS:

      A. Distributions:

         The only permissible form of distribution shall be a lump-sum made
         pursuant to Section 7.08(a)(1).

      B. Financial Hardship Withdrawals of Salary Deposit Amounts:

         1.       Financial Hardship Withdrawals shall be allowed.

         2.       The permissible reasons for obtaining a Financial Hardship
                  Withdrawal shall be those permitted under Section 7.11(b).

         3.       The resources readily available shall be determined based on
                  the facts and circumstances as described in Section 7.11(d)
                  of the plan. The appropriate documentation from a third party
                  regarding the types and amounts of the expenses relating to
                  the Financial Hardship Withdrawal, must be provided by
                  Participants, as described in Section 7.11(b) of the Plan.

      C. In-Service Withdrawals:

         As of the date that a Participant attains the age of 59 1/2, the
         Participant may withdraw his Vested Balance.

      D. Disability:

         A Participant's Disability under the Plan shall be determined pursuant
         to Section 7.04(b)(2) of the Plan.

      E. Early Retirement:

         Participants may retire upon the attainment of age 55 and may elect to
         receive Normal Retirement Benefits pursuant to Section 7.02 of the
         Plan.

                                       v



<PAGE>   6




VIII. JOINT AND SURVIVOR ANNUITY REQUIREMENTS:

      Article VIII of the basic Plan document, the Joint and Survivor Annuity
provisions, shall not apply to the Plan.

IX.   OTHER PLANS OF THE EMPLOYER:

      A. The Employer does not maintain another qualified defined contribution
         plan.

      B. The Employer maintains a qualified defined benefit plan, the Mid
         Louisiana Gas Company Pension Plan.

         1.       Notwithstanding any provisions in Section 5.02 or 5.03 to the
                  contrary, in the event that for any Plan Year the defined
                  benefit plan fraction and the defined contribution plan
                  fraction (as described in Code Section 415(c) and Article V of
                  the Plan) shall be exceeded for an Employee participating in
                  this Plan and the Mid Louisiana Gas Company Pension Plan, any
                  reductions necessary to meet the requirements of Code Section
                  415(e) and Article V of the Plan shall be made under the Mid
                  Louisiana Gas Company Pension Plan.
      
         2.       Pursuant to the provisions of the Plan Section 9.05, the Mid
                  Louisiana Gas Company Pension Plan shall, provided such plan
                  is in the Required Aggregation Group of the Employer, provide
                  the maximum benefit required under Code Section 416.

X.    AFFILIATED EMPLOYERS:

      The Employer has the following Affiliates (as defined in Section 1.04 of
the Plan):

           Mid Louisiana Gas Company

XI.   INVESTMENTS:

      A. The Employer shall designate the Investment Options available under the
         Plan.

      B. The Plan is intended to be an ERISA Section 404(c) plan. Participants
         may elect or designate their Investment Options from among the
         Investment Alternatives selected by the Employer to be available under
         the Plan. A Participant may direct the investment of all amounts in all
         of his/her accounts.

      C. Life Insurance Contracts shall not be offered to Participants.

XII   PLAN LOANS:

       Plan Loans shall be permitted.

                                       vi





<PAGE>   7




XIII. PARTICIPATING EMPLOYERS:

      Mid Louisiana Gas Company is a Participating Employer, pursuant to Article
XVI of the Plan.

      This Adoption Agreement shall only be used in conjunction with the basic
plan document identified as the Coho Resources, Inc. 401(k) Savings Plan.

      IN WITNESS WHEREOF, the Employer and the Trustee have executed this
Adoption Agreement and Plan on the day and year first written.

                                        EMPLOYER:

ATTEST By: /s/ LAURIE SUPTON            Coho Resources, Inc.
         ---------------------------   

                                        R. Lynn Guillory
                                        --------------------------------------
                                        Name


                                        Vice President - Human Resources &
                                        Administration
                                        --------------------------------------
                                        Title


                                        /s/ R. LYNN GUILLORY
                                        --------------------------------------
                                        Signature  



ATTEST By: /s/ LAURIE SUPTON            TRUSTEE:
         ---------------------------   
                                        

                                        /s/ R. LYNN GUILLORY
                                        --------------------------------------
                                        R. Lynn Guillory


                                        /s/ JOSEPH R. RAGUSA
                                        --------------------------------------
                                        Joseph R. Ragusa    

                                        /s/ SUSAN MCADEN
                                        --------------------------------------
                                        Susan McAden



                                      vii



<PAGE>   8





                                SPECIAL AMENDMENT
                                     TO THE
                              COHO RESOURCES, INC.
                               401(k) SAVINGS PLAN

         This Special Amendment to the Coho Resources, Inc. 401(k) Savings
Plan (hereinafter referred to as the "Plan") is hereby executed and adopted on
this 8th day of December, 1997, by Coho Resources, Inc. (hereinafter referred to
as the "Employer") and Joseph F. Ragusa, R. Lynn Guillory and Susan McAden 
(hereinafter referred to as "Trustee").

                               W I T N E S S E T H

         WHEREAS, the Employer has heretofore maintained and administered the
Plan and related Trust, in a manner intended to ensure that the Plan continues
to qualify under Sections 401(a) and 501(a) of the Internal Revenue Code of
1986; and

         WHEREAS, pursuant to the terms of the Plan, the Employer reserved the
right to amend the Plan; and

         WHEREAS, the Employer desires to amend the Plan to comply with
requirements of the Uniformed Services Employment and Reemployment Rights Act of
1994 ("USERRA"); and

         WHEREAS, the Employer desires to amend the Plan to comply with the
minimum distribution provisions of the Small Business Job Protection Act of 1996
("SBJPA"); and

         WHEREAS, the Employer desires to amend the Plan to increase the maximum
involuntary cashout amount to $5,000, as provided in the Taxpayer Relief Act of
1997 ("TRA of 97");

         NOW THEREFORE, in consideration of the premises and mutual covenants
contained herein the Employer hereby amends the Plan notwithstanding any other
provision of the Plan to the contrary as follows:

                                       I.

Effective January 1, 1997:

Notwithstanding any other provision of this plan to the contrary, minimum
distributions shall be made in accordance with Section 401(a)(9) of the Internal
Revenue Code.

                                      II.

Effective January 1, 1998:

Notwithstanding any other provision of this plan to the contrary, if the value
of the Vested benefit of a Participant who has Separated from Service does not
exceed $5,000, the Plan Administrator shall direct the Trustee to cause the
entire Vested benefit to be paid to such Participant in a single lump sum.



<PAGE>   9

                                      III.

 Effective December 12, 1994:

A.       Notwithstanding any provision of this plan to the contrary,
         contributions, benefits and service credit with respect to qualified
         military service will be provided in accordance with Section 414(u) of
         the Internal Revenue Code.

B.       Loan repayments will be suspended under this plan as permitted under
         Section 414(u)(4) of the Internal Revenue Code.

                                      IV.

In all other respects, the Plan is hereby ratified and affirmed.


                                    COHO RESOURCES, INC.

                                    By: /s/ R. LYNN GUILLORY  
                                       --------------------------------------  
                                        
                                        
                                    Title: Vice President - Human Resources &
                                           Administration       
                                           ----------------------------------  
                                                                       
                                        
                                    TRUSTEE:                                
                                        

                                        
                                    /s/ JOSEPH R. RAGUSA                    
                                    --------------------------------------  
                                    Joseph R. Ragusa                        

                                        
                                    /s/ R. LYNN GUILLORY                    
                                    --------------------------------------  
                                    R. Lynn Guillory                        
                                        
                                        
                                    /s/ SUSAN MCADEN                        
                                    --------------------------------------  
                                    Susan McAden                            




<PAGE>   10





                          UNANIMOUS WRITTEN CONSENT OF
                                 THE TRUSTEES OF
                    COHO RESOURCES, INC. 401(k) SAVINGS PLAN

The undersigned, being all of the duly elected and qualified Trustees of the
Coho Resources, Inc. 401(k) Savings Plan (hereinafter referred to as the
"Plan"), and acting pursuant to the authority granted them by Coho Resources,
Inc. (hereinafter referred to as the "Company"), do hereby execute this
Unanimous Consent for the purpose of taking the following actions and the
adoption of the following resolutions as the actions of the Company, as of the
date hereof:

         WHEREAS, the Company has heretofore maintained and administered the
Coho Resources, Inc. 401(k) Savings Plan (hereinafter referred to as the
"Plan"), in a manner intended to ensure that the Plan continues to qualify
under Sections 401(a) and 501(a) of the Internal Revenue Code of 1986; and

         WHEREAS, pursuant to the terms of the Plan, the Company reserved the
right to amend the Plan; and

         WHEREAS, the Company desires to amend the Plan to comply with
requirements of the Uniformed Services Employment and Reemployment Rights Act of
1994 ("USERRA"); and

         WHEREAS, the Company desires to amend the Plan to comply with the
minimum distribution provisions of the Small Business Job Protection Act of 1996
("SBJPA"); and

         WHEREAS, the Company desires to amend the Plan to increase the maximum
involuntary cash-out amount to $5,000, as provided in the Taxpayer Relief Act of
1997 ("TRA of 97");

         WHEREAS, the Company shall amend the Plan for the above law changes as
a Special Amendment, unless otherwise indicated with a numbered amendment.

         NOW, THEREFORE BE IT RESOLVED, that the Special Amendment attached
hereto as Exhibit A is adopted and is hereby incorporated by reference.

This Unanimous Written Consent may be executed in more than one counterpart and
such counterparts when taken together shall constitute one consent.

Any third party dealing with the Corporation shall be entitled to rely on a copy
or facsimile of this consent rather than an original hereof.

EXECUTED this ________________ day of _______________, 1997.
                

                                    TRUSTEES:

                                    /s/ JOSEPH R. RAGUSA                    
                                    --------------------------------------  
                                    Joseph R. Ragusa                        

                                        
                                    /s/ R. LYNN GUILLORY                    
                                    --------------------------------------  
                                    R. Lynn Guillory                        
                                        
                                        
                                    /s/ SUSAN MCADEN                        
                                    --------------------------------------  
                                    Susan McAden                            





<PAGE>   11




                              COHO RESOURCES, INC.

                Consent of Directors in Lieu of Special Meeting

         Pursuant to Section 78.315 of the Nevada General Corporation Law, the
undersigned, being the all of the members of the Board of Directors of Coho
Resources, Inc., a Nevada corporation (the "Company") and in lieu of a special
meeting of directors, the call of which is hereby expressly waived, does hereby
consent to the adoption of and does hereby adopt the resolutions set forth in
Exhibit A hereto.


Dated as of December 3, 1998                    DIRECTORS



                                                /s/ JEFFREY CLARKE
                                                -------------------------------
                                                Jeffrey Clarke


                                                /s/ RICK PEARCE
                                                -------------------------------
                                                Rick Pearce



<PAGE>   12



                                                            EXHIBIT A

         WHEREAS, October 5, 1990, in recognition of the contributions made by
its employees to its successful operations, the Company established a defined
contribution profit sharing plan and trust, known as the Coho Resources, Inc.
401(k) Savings Plan (which plan and trust are hereinafter referred to as the
"Plan"), for the exclusive benefit of eligible employees of the Company; and

         WHEREAS, the Company has heretofore maintained the Plan in a manner
intended to ensure that the Plan qualifies under Sections 401(a) and 501(a) of
the Internal Revenue Code of 1986, as amended (the "Code"); and

         WHEREAS, Section 15.04 of the Plan provides for full vesting for Plan
Participants who are affected by a partial termination of the Plan; and

         WHEREAS, effective December 2, 1998, the Company shall provide for the
full vesting of benefits and accounts under the Plan for Plan Participants whose
employment with the Company was terminated as a result of the sale of a
subsidiary division of Coho known as Coho Louisiana Production Company
(hereinafter referred to as "The Division") to a partnership managed by EnerVest
Management Company without regard to whether the sale of said division
constituted a partial termination of the Plan under the Code; and

         WHEREAS, the sum of the account balances for each participant employed
by The Division shall equal the fair market value of the assets that each
participant had ON December 2, 1998 as each participant had in the plan
immediately prior to the sale; and

         NOW, THEREFORE, BE IT RESOLVED, that due to sale of The Division to
EnerVest Management Company, Plan Participants employed at The Division, whose
employment was involuntarily terminated due to the sale of The Division, shall
become fully vested in all of their benefits and accounts under the Plan,
effective as of the date of such sale, without regard to whether said sale
constitutes a partial termination of the Plan under the Code; and

         FURTHER RESOLVED, the sum of the account balances for each participant
employed by The Division shall equal the fair market value of the assets that
each participant had on December 2, 1998 as each participant had in the plan
immediately prior to the sale; and

          FURTHER RESOLVED, that a conformed copy of this UNANIMOUS WRITTEN



<PAGE>   13



CONSENT shall constitute an appendix to the Plan, to be maintained as a record
of historical reference; and

         FURTHER RESOLVED, that the proper officers of the Company be, and they
hereby are, authorized and empowered to file any applications with the Internal
Revenue Service which such officers shall deem necessary or appropriate,
together with any supporting documentation, in securing a determination that
said action shall not cause the Plan, as hereby amended, to fail to meet the
requirements of Section 401(a) and 501(a) of the Code, and that said Plan
continues to be qualified, and to execute such powers of attorney, schedules and
other documents as may be necessary or desirable in connection therewith; and

         FURTHER RESOLVED, that the acts and deeds of the proper officers of the
Company necessary to effectuate the intent and purpose of these resolutions be,
and the same hereby are, ratified, confirmed, and adopted as the acts and deeds
of the Company.