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                                                                   EXHIBIT 10.56



                             RENEWAL PROMISSORY NOTE

$3,370,694.12                    Houston, Texas                      May 1, 1998

         FOR VALUE RECEIVED, the undersigned, FUTURE PETROLEUM CORPORATION, a
Utah corporation, hereby promises to pay to the order of ENERGY CAPITAL
INVESTMENT COMPANY PLC, an English investment company ("Lender") the principal
sum of THREE MILLION THREE HUNDRED SEVENTY THOUSAND SIX HUNDRED NINETY-FOUR AND
12 /100 Dollars ($3,370,694.12) with interest on the unpaid balance thereof from
the date hereof until maturity at the rate of ten percent (10%) per annum, both
principal and interest payable as hereinafter provided in lawful money of the
United States of America at 1100 Louisiana, Suite 3150, Houston, Texas 77002, or
at such other place within Harris County, Texas as from time to time may be
designated by the holder of this Note.

         All past due principal and/or interest or installments thereof shall
bear interest at the highest rate for which the undersigned may legally contract
under applicable law or, if no such rate is designated under applicable law, at
the rate of eighteen percent (18%) per annum.

         Interest only on this Note shall be due and payable monthly as it
accrues on the last business day of each month, beginning May 29, 1998 and on
the last business day of each succeeding month through and including December
31, 1998. Thereafter: (i) the principal of this Note shall be due and payable in
monthly installments of Thirty-Five Thousand One Hundred Eleven and 39/100
Dollars ($35,111.39) each, payable on the last business day of each calendar
month, beginning January 31, 1999, and continuing regularly thereafter until and
including December 31, 2003, on which date all unpaid principal of and accrued
interest on this Note shall be due and payable and (ii) interest shall be due
and payable monthly as it accrues, on the same dates as, but in addition to,
said installments of principal.

         This Note (a) is executed and delivered in connection with and pursuant
to that certain Purchase and Sale Agreement dated November 25, 1997 (as now or
hereafter amended, supplemented, or restated the "November 1997 Purchase
Agreement") between the undersigned and Energy Capital Investment Company PLC,
EnCap Equity 1994 Limited Partnership and Gecko Booty 1994 I Limited Partnership
and is one of the "Notes" as defined therein, (b) is executed and delivered in
connection with and pursuant to that certain Purchase and Sale Agreement dated
May 1, 1998 (as now or hereafter amended, supplemented, or restated, the "May
1998 Purchase Agreement) between the undersigned and Energy Capital Investment
Company PLC, EnCap Equity 1994 Limited Partnership and NCI Enterprises, Inc.,
and is one of the "Notes" as defined therein, (c) is subject to the terms and
provisions thereof, which contains provisions for acceleration of maturity
hereof upon the happening of certain stated events, and (d) is secured by and
entitled to the benefits of certain security documents (as identified therein).
Reference is hereby made to (i) the November 1997 Purchase Agreement and the May
1998 Purchase Agreement for a description of certain rights, limitations of
rights, obligations and duties of the parties hereto and for the meanings
assigned to terms used and not defined herein, and (ii) the security documents
referenced above for a description of the nature and extent of the security
thereby provided and the rights of the parties thereto.



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         This Note is in renewal, extension and increase, but not in novation or
extinguishment, of that certain Promissory Note dated November 25, 1997 executed
by the undersigned and payable to the order of Lender in the original principal
amount of $3,123,041.

         The undersigned shall have the right to prepay, without penalty, at any
time and from time to time prior to maturity, all or any part of the unpaid
principal balance of this Note and/or all or any part of the unpaid interest
accrued to the date of such prepayment, provided that any such principal thus
paid is accompanied by accrued interest on such principal. Any partial
prepayments of principal shall be applied to installments thereof in the inverse
order of maturity.

         It is the intent of the payee of this Note and the undersigned in the
execution of this Note and all other instruments now or hereafter securing this
Note to contract in strict compliance with applicable usury law. In furtherance
thereof, the said payee and the undersigned stipulate and agree that none of the
terms and provisions contained in this Note, or in any other instrument executed
in connection herewith, shall ever be construed to create a contract to pay for
the use, forbearance or detention of money, interest at a rate in excess of the
maximum interest rate permitted to be charged by applicable law; that neither
the undersigned nor any guarantors, endorsers or other parties now or hereafter
becoming liable for payment of this Note shall ever be obligated or required to
pay interest on this Note at a rate in excess of the maximum interest that may
be lawfully charged under applicable law; and that the provisions of this
paragraph shall control over all other provisions of this Note and any other
instruments now or hereafter executed in connection herewith which may be in
apparent conflict herewith. The holder of this Note expressly disavows any
intention to charge or collect excessive unearned interest or finance charges in
the event the maturity of this Note is accelerated. If the maturity of this Note
shall be accelerated for any reason or if the principal of this Note is paid
prior to the end of the term of this Note, and as a result thereof the interest
received for the actual period of existence of the loan evidenced by this Note
exceeds the applicable maximum lawful rate, the holder of this Note shall, at
its option, either refund to the undersigned the amount of such excess or credit
the amount of such excess against the principal balance of this Note then
outstanding and thereby shall render inapplicable any and all penalties of any
kind provided by applicable law as a result of such excess interest. In the
event that the said payee or any other holder of this Note shall contract for,
charge or receive any amount or amounts and/or any other thing of value which
are determined to constitute interest which would increase the effective
interest rate on this Note to a rate in excess of that permitted to be charged
by applicable law, an amount equal to interest in excess of the lawful rate
shall, upon such determination, at the option of the holder of this Note, be
either immediately returned to the undersigned or credited against the principal
balance of this Note then outstanding, in which event any and all penalties of
any kind under applicable law as a result of such excess interest shall be
inapplicable. By execution of this Note the undersigned acknowledges that it
believes the loan evidenced by this Note to be non-usurious and agrees that if,
at any time, the undersigned should have reason to believe that such loan is in
fact usurious, it will give the holder of this Note notice of such condition and
the undersigned agrees that said holder shall have ninety (90) days in which to
make appropriate refund or other adjustment in order to correct such condition
if in fact such exists. The term "applicable 



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law" as used in this Note shall mean the laws of the State of Texas or the laws
of the United States, whichever laws allow the greater rate of interest, as such
laws now exist or may be changed or amended or come into effect in the future.

         Should the indebtedness represented by this Note or any part thereof be
collected at law or in equity or through any bankruptcy, receivership, probate
or other court proceedings or if this Note is placed in the hands of attorneys
for collection after default, the undersigned and all endorsers, guarantors and
sureties of this Note jointly and severally agree to pay to the holder of this
Note in addition to the principal and interest due and payable hereon all the
costs and expenses of said holder in enforcing this Note including, without
limitation, reasonable attorneys' fees and legal expenses.

         The undersigned and all endorsers, guarantors and sureties of this Note
and all other persons liable or to become liable on this Note severally waive
presentment for payment, demand, notice of demand and of dishonor and nonpayment
of this Note, notice of intention to accelerate the maturity of this Note,
protest and notice of protest, diligence in collecting, and the bringing of suit
against any other party, and agree to all renewals, extensions, modifications,
partial payments, releases or substitutions of security, in whole or in part,
with or without notice, before or after maturity.

         THIS NOTE AND THE RIGHTS AND DUTIES OF THE PARTIES HEREUNDER SHALL BE
GOVERNED FOR ALL PURPOSES BY THE LAW OF THE STATE OF TEXAS AND THE LAW OF THE
UNITED STATES APPLICABLE TO TRANSACTIONS WITHIN SUCH STATE.

                                           FUTURE PETROLEUM CORPORATION,
                                            a Utah corporation



                                           By: /s/ B. CARL PRICE
                                              ---------------------------------
                                               B. Carl Price, President



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