<PAGE>   1
                                                                    EXHIBT 10.2


                                    GUARANTY


         This GUARANTY is made and entered into as of the Effective Date (as
defined below) by SEAGULL ENERGY CORPORATION, a Texas corporation
("Guarantor"), in favor of the Beneficiaries (as defined below).

                                   RECITALS:

         1.      Guarantor owns all of the issued and outstanding common stock
of Seagull Energy E&P Inc., a Delaware corporation ("Seagull E&P").

         2.      Seagull E&P, as Depositor, initial Series B Holder and
Managing Trustee, Mark A. Ferrucci, as Special Trustee, and FC Energy Finance
I, Inc., a Delaware corporation ("FC Energy"), and Carthage Field Corp., a
Delaware corporation ("Carthage"), as Series A Holders, are this day forming
Seagull Series 1995 Trust as a Delaware business trust (the "Trust") pursuant
to that certain Trust Agreement, of even date herewith (the "Trust Agreement").
Capitalized terms that are used but not defined herein shall have the meanings
given them in the Trust Agreement.

         3.      Seagull E&P is the Depositor, Managing Trustee and the initial
Series B Holder and FC Energy and Carthage are the initial Series A Holders.
For the purposes hereof, "Beneficiaries" shall mean collectively, the Series A
Holders, the Trust and the Trustees (unless such Trustee is an Affiliate of
Guarantor).  As used herein, the term "Obligor" shall mean Seagull E&P,
Mid-South, Midcon and each other Person that (a) becomes a Holder, Managing
Trustee or an Operator Affiliate and (b) at such time is an Affiliate of
Guarantor.

         NOW THEREFORE, to induce the Beneficiaries to enter into the Trust
Agreement, Guarantor agrees as follows:


                                   ARTICLE 1
                                    GUARANTY

         1.1     GUARANTY.  Guarantor hereby irrevocably, absolutely and
unconditionally guarantees the full and prompt payment by Obligor of all
amounts that Obligor may become obligated to pay under the Trust Agreement, any
Assignment or any Operating Agreement, including any payments due under
Sections 5.5, 6.5, 7.9 and 7.11 and Article 9 of the Trust Agreement and money
damages arising from any failure by an Obligor to perform any non-payment
obligation (the "Obligations").
<PAGE>   2
         1.2     IRREVOCABILITY.  This Guaranty is an irrevocable and
continuing guaranty that will remain in full force and effect until all of the
Obligations are either paid in full or otherwise fully and finally discharged
and satisfied, at which time this Guaranty shall automatically terminate.

         1.3     NATURE OF GUARANTY.  (a)  This Guaranty is a guaranty of
payment and not of collection.  Accordingly, the Beneficiaries need not enforce
any rights or remedies they may have against any Obligor before exercising
their rights against Guarantor under this Guaranty.

         (b)     Being a guaranty of payment, this Guaranty is not a guaranty
of performance and does not obligate Guarantor to perform any non-payment
obligations of Obligor under the Trust Agreement, any Assignment or any
Operating Agreement, except to the extent that any failure by Obligor to
perform any such non-payment obligation has evolved into a payment obligation
under the Trust Agreement, any Assignment or any Operating Agreement.

         1.4     WAIVERS.  Guarantor hereby waives (a) presentment, demand,
protest, promptness and diligence with respect to the Obligations and this
Guaranty, (b) any right of subrogation it may have against Obligor with respect
to any payment Guarantor makes under this Guaranty, and (c) notices of all
kinds with respect to the Obligations and this Guaranty, including (i) notice
of protest, non-payment, default and dishonor, (ii) any notices with respect to
any of the events described in Section 1.5, and (iii) notice of acceptance of
this Guaranty (acceptance on the part of the Beneficiaries being conclusively
presumed by the Initial Series A Holders' and the Trust's request for this
Guaranty and delivery of the same to them).

         1.5     GUARANTY UNAFFECTED BY CERTAIN EVENTS.  The obligations of
Guarantor under this Guaranty are absolute and unconditional, irrespective of
any lack of value, genuineness, validity, legality, regularity or
enforceability of the Trust Agreement or any part of the Obligations or any
agreement or instrument relating to the Obligations, or any substitution,
release or exchange of any other guarantee of or security for any of the
Obligations, and, to the fullest extent permitted by applicable Law,
irrespective of any other circumstance whatsoever that might otherwise
constitute a legal or equitable discharge or defense of a surety or guarantor;
Guarantor shall, however, have the benefit of and the right to assert any
defenses against the claims of any Beneficiary which are available to any
Obligor (other than any defenses arising out of or relating to the bankruptcy,
insolvency or dissolution of any Obligor).  Without limiting the generality of
the foregoing, it is agreed that this Guaranty will not be released,
terminated, diminished, impaired or otherwise affected by the occurrence of any
of the following events:

                 (a)      any amendment or other modification of the Trust
         Agreement, the Assignments or the Operating Agreements, including any
         increase, decrease, extension, renewal, rearrangement or other
         amendment or modification of any of the Obligations;




                                     -2-
<PAGE>   3
                 (b)      any failure of the Beneficiaries to exercise their
         rights under the Trust Agreement, any delay by the Beneficiaries in
         exercising such rights; or any release, waiver, adjustment,
         indulgence, forbearance or compromise with respect to such rights;

                 (c)      the creation or existence of any other guaranty,
         security, collateral or other assurance of payment for the repayment
         of all or any of the Obligations ("Additional Security"); any failure
         of the Beneficiaries to exercise such rights; any delay by the
         Beneficiaries in exercising such rights, including any deterioration
         of any Additional Security caused thereby; any release, waiver,
         adjustment, indulgence, forbearance or compromise with respect to such
         rights; any failure of any such Additional Security to be properly
         created or perfected; any subordination of any Additional Security;

                 (d)      any failure to join any Obligor in any suit under
         this Guaranty, and any failure to join Guarantor in any suit with
         respect to the Obligations or any Additional Security;

                 (e)      any Transfer by a Beneficiary of its rights,
         interests and obligations under the Trust Agreement, this Guaranty or
         any Additional Security;

                 (f)      any consent to any Transfer by any Obligor of its
         rights, interests and obligations under the Trust Agreement;

                 (g)      any Bankruptcy, insolvency or dissolution of any
         Obligor;

                 (h)      any other action taken or omitted to be taken with
         respect to the Obligations or the Additional Security, whether or not
         such action or omission prejudices Guarantor or increases the
         likelihood that Guarantor will be required to pay the Obligations
         pursuant to the terms hereof;

                 (i)      any merger or consolidation of, sale of substantial
         assets by or other restructuring or termination of the corporate
         existence of Guarantor or any Obligor into or with any other Person,
         or any consent thereto;

                 (j)      any change in the beneficial ownership of or
         interests in Guarantor or any Obligor; or

                 (k)      any regulatory change or other governmental action.





                                      -3-
<PAGE>   4
         1.7     RETURNED PAYMENTS.  This Guaranty will continue to be
effective or be automatically reinstated, as the case may be, if any payment of
any of the Obligations is rescinded, or must otherwise be returned by any
Beneficiary, for any reason, including the Bankruptcy of any Obligor, all as
though such payment had not been made.  In such event, Guarantor shall pay to
such Beneficiary an amount equal to any such payment that has been rescinded or
returned and shall indemnify such Beneficiary on demand for all reasonable
costs and expenses (including reasonable attorneys' fees) incurred by such
Beneficiary in connection with its compliance with or reasonable resistance to
any such rescission or return.

         1.8     REPRESENTATIONS AND WARRANTIES.  Guarantor represents and
warrants to, and agrees with, the Beneficiaries as follows:

                 (a)      Guarantor is duly incorporated, validly existing and
         in good standing under the Laws of the State of Texas.  Guarantor has
         the right, power and authority to enter into this Guaranty and to
         perform its obligations hereunder.

                 (b)      The execution, delivery and performance of this
         Guaranty by Guarantor (i) have been duly authorized by all requisite
         corporate action of Guarantor, (ii) do not violate or conflict with
         the Articles of Incorporation or Bylaws of Guarantor or any Law,
         material contract or material obligation applicable to Guarantor or
         any of its properties, and (iii) do not require any material consent,
         approval, authorization or order of any Governmental Authority or
         other Person with respect to the Guarantor, except for ones that have
         been previously obtained.

                 (c)      This Guaranty represents legal, valid and binding
         obligations of Guarantor.

                 (d)      The execution and delivery of the Trust Agreement,
         the Assignments and the New Operating Agreements is reasonably
         expected to benefit, directly or indirectly, Guarantor.

                 (e)      Guarantor has established adequate means of obtaining
         financial and other information pertaining to the business, operations
         and condition (financial and otherwise) of Obligor and the Assets on a
         continuing basis and Guarantor is now and will in the future remain
         fully familiar with the business, operations and condition (financial
         and otherwise) of Obligor and the Assets.  Guarantor further
         represents and warrants that it is familiar with the transactions
         contemplated by the Trust Agreement and that it will in the future
         remain fully familiar with such transactions and with any new,
         amended, modified or revised Trust Agreement and the transactions
         contemplated thereby.  Guarantor hereby expressly waives and
         relinquishes any duty on the part of any Beneficiary (should any such
         duty exist) to disclose to Guarantor any matter of fact or other
         information related to the business,





                                      -4-
<PAGE>   5
         operations or condition (financial or otherwise) of Obligor or the
         Assets or to the Trust Agreement or the transactions undertaken
         pursuant to, or contemplated by, such Trust Agreement, whether now or
         in the future known by any Beneficiary.

         1.9     CONTROL OF OBLIGOR.  Guarantor agrees that it will not cease
to control any Obligor, directly or indirectly, other than (i) in the case of
Seagull E&P, as contemplated in Section 4.2(f)(ii) of the Trust Agreement, and
(ii) in the case of any other Obligor, in a transaction that would be permitted
under Section 4.2(f)(ii) of the Trust Agreement if such Obligor were the Series
B Holder under such Section 4.2(f)(ii).

         1.10    SUBORDINATION.  Guarantor hereby subordinates any and all
indebtedness of Obligor owing to it, whether now existing or hereafter arising,
to the full and final satisfaction by Obligor of all of the Obligations.

         1.11    ENFORCEMENT.  Guarantor hereby agrees to pay all costs and
expenses, including reasonable attorneys' fees and disbursements, incurred by
any Beneficiary in the enforcement of any and all terms of this Guaranty after
a claim for payment has been made against Guarantor.

         1.12    TERMINATION.  This Guaranty shall terminate as to any
Obligations of any Obligor arising after the time that Guarantor ceases to
Control such Obligor in accordance with the provisions of Section 1.9.

                                   ARTICLE 2
                               GENERAL PROVISIONS

         2.1     NOTICES.  All notices, requests, or consents to Guarantor
under this Guaranty must be in writing and must be given either by depositing
that writing in the United States mail, addressed to Guarantor, postage paid,
and registered or certified with return receipt requested or by delivering that
writing to Guarantor in person, by courier, or by facsimile transmission, at
the following address (or such other address as Guarantor may specify by notice
to the Beneficiaries):

         Seagull Energy Corporation
         1001 Fannin, Suite 1700
         Houston, Texas  77002-6714
         Attention:   Vice President, Corporate Development
                             and Treasurer
         Fax:         (713) 951-4846

A notice, request, or consent given under this Guaranty is effective on receipt
at such address.





                                      -5-
<PAGE>   6
         2.2     ENTIRE GUARANTY; SUPERSEDURE.  This Guaranty constitutes the
entire agreement of Guarantor and the Beneficiaries relating to the guarantee
of the Obligations and supersedes all prior contracts or agreements with
respect to thereto, whether oral or written, including those certain letter
agreements dated May 26, 1995 and July 5, 1995, between an Affiliate of FC
Energy and Guarantor.

         2.3     EFFECT OF WAIVER OR CONSENT.  A waiver or consent, express or
implied, to or of any breach or default by Guarantor in the performance of its
obligations hereunder is not a consent or waiver to or of any other breach or
default in the performance by Guarantor of any other obligations of Guarantor
hereunder.  Failure on the part of the Beneficiaries to complain of any act of
Guarantor or to declare Guarantor in default with respect hereunder,
irrespective of how long that failure continues, does not constitute a waiver
by the Beneficiaries of their rights with respect to that default until the
applicable statute-of-limitations period has run.

         2.4     AMENDMENT OR MODIFICATION.  This Guaranty may be amended or
modified from time to time only by a written instrument executed by Guarantor
and the Series A Supermajority Interest.

         2.5     BINDING EFFECT.  This Guaranty (a) is binding on Guarantor and
its successors and assigns, and (b) subject to the restrictions on Transfers
set forth in the Trust Agreement, will inure to the benefit of the
Beneficiaries and their respective legal representatives, successors, and
assigns.

         2.6     GOVERNING LAW; SEVERABILITY.  THIS GUARANTY IS GOVERNED BY AND
WILL BE CONSTRUED IN ACCORDANCE WITH THE LAW OF THE STATE OF TEXAS, EXCLUDING
ANY CONFLICT-OF-LAWS RULE OR PRINCIPLE THAT MIGHT REFER THE GOVERNANCE OR THE
CONSTRUCTION OF THIS GUARANTY TO THE LAW OF ANOTHER JURISDICTION.  If any
provision of this Guaranty or its application to any circumstance is held
invalid or unenforceable to any extent, the remainder of this Guaranty and the
application of that provision to other circumstances is not affected and that
provision will be enforced to the greatest extent permitted by applicable Law.

         EXECUTED as of the Effective Date.

                                   SEAGULL ENERGY CORPORATION


                                   By:  /s/ ROBERT M. KING
                                       -----------------------------------------
                                       Robert M. King
                                       Vice President, Corporate Development and
                                       Treasurer





                                      -6-