<PAGE>   1
                                                                   EXHIBIT 10.1

                                AMENDMENT NO. 1

                 AMENDMENT NO. 1 dated as of April 15, 1997 (this "Amendment"),
between RUTHERFORD--MORAN OIL CORPORATION, a Delaware corporation (the
"Borrower"); RUTHERFORD--MORAN EXPLORATION COMPANY, a Delaware corporation;
THAI ROMO HOLDINGS, INC., a Delaware corporation; THAI ROMO LIMITED, a company
organized under the laws of the Kingdom of Thailand (collectively, the
"Subsidiary Guarantors"); and The Chase Manhattan Bank, a New York State
banking corporation (the "Bank").

                 The Borrower, the Subsidiary Guarantors and the Bank are
parties to a Credit Agreement dated as of February 26, 1997 (the "Credit
Agreement"), providing, subject to the terms and conditions thereof, for a loan
to be made by the Bank to the Borrower in a principal amount up to but not
exceeding $20,000,000.  The Borrower, the Subsidiary Guarantors and the Bank
wish to amend the Credit Agreement in certain respects, and accordingly, the
parties hereto agree as follows:

                 Section 1.  Definitions.  Except as otherwise defined in this
Amendment No. 1, terms defined in the Credit Agreement are used herein as
defined therein.

                 Section 2.  Amendments.  Subject to the satisfaction of the
conditions precedent specified in Section 4 below, but effective as of the date
hereof, the Credit Agreement shall be amended as follows:

                 2.01.  References in the Credit Agreement (including
references to the Credit Agreement as amended hereby) to "this Agreement" (and
indirect references such as "hereunder", "hereby", "herein" and "hereof") shall
be deemed to be references to the Credit Agreement as amended hereby.

                 2.02.  The definition of "Commitment" in Section 1.01 of the
Credit Agreement is amended by deleting $20,000,000 from the third line and
substituting $25,000,000 in place thereof.

                 2.03.      The definition of ""Scheduled Commitment
Termination Date" is deleted and replaced as follows: "Scheduled Commitment
Termination Date" shall mean three Business Days after the date of this
Amendment.

                 2.04.  The following definition is hereby added in
alphabetical order in Section 1.01 of the Credit Agreement:

                 "Thai-Tex" shall mean Thai-Tex Insurance Company, a captive
insurance company organized under the laws of the State of Hawaii, and a
wholly-owned Subsidiary of the Borrower.

                 2.05.  Section 8.21 of the Credit Agreement is amended by (x)
deleting the word "the" at the end of the first line and inserting in place
thereof "$20,000,000 of" and (y) adding the following sentence at the end of
Section 8.21:
<PAGE>   2
                 "Proceeds of the Loan hereunder in excess of $20,000,000 may
                 be used for general corporate purposes of the Borrower or any
                 Subsidiary Guarantor."

                 2.06.      Section 9.04 of the Credit Agreement is amended by
adding immediately after the words "similarly situated," the words "and may
reinsure such risks with Thai-Tex".

                 2.07.      Section 9.07 of the Credit Agreement is amended by
(x) deleting the word "and" at the end of clause (j) therein and (y) adding a 
new clause (k) as follows:

                 "(k)     Indebtedness of Thai-Tex in respect of loans and
                          advances made as permitted by Section 9.08(j); and"

and (z) changing existing clause "(k)" therein to clause "(l)".

                 2.08.  Section 9.08 of the Credit Agreement is amended by (x)
deleting the word "and" at the end of clause (i) therein and (y) adding a new
clause (j) as follows:

                 "(j)     loans and advances by the Borrower to Thai-Tex, up to
                          but not exceeding $3,000,000 in the aggregate, and
                          Investments by the Borrower in common stock of
                          Thai-Tex and other capital contributions by the
                          Borrower to Thai-Tex up to but not exceeding $500,000
                          in the aggregate; and"

and (z) changing existing clause "(j)" therein to clause "(k)".

                 2.09.  Section 9.11 of the Credit Agreement is hereby amended
by adding the following sentence at the end of Section 9.11:

                 "Notwithstanding the foregoing, Thai-Tex may engage in the
                 business of a reinsurance captive."

                 2.10.  Section 9.13 of the Credit Agreement is amended by
adding ", (j) and (k)" immediately following the phrase "Section 9.08(g)"
therein.

                 Section 3.  Representations and Warranties.  Each of the
Borrower and the Subsidiary Guarantors represents and warrants to the Bank that
after giving effect to this Amendment No. 1 and the making of the additional
Loan contemplated hereunder,

                 (a)      no Default shall have occurred and be continuing; and

                 (b)      the representations and warranties made by the
                 Obligors in Section 8 of the Credit Agreement and by each





                                     -2-
<PAGE>   3
                 Obligor in each of the Basic Documents to which such Obligor
                 is a party, are true and correct on and as of the date hereof
                 with the same force and effect as if made on and as of the
                 date hereof (or, if any such representation or warranty is
                 expressly stated to have been made as of a specific date, as
                 of such specific date).

                 Section 4.  Conditions Precedent.  The amendments to the
Credit Agreement set forth in Section 2 hereof shall become effective, as of
the date hereof, upon the satisfaction of the following conditions precedent:

                 4.01.  Execution by All Parties.  This Amendment No. 1 shall
have been executed and delivered by the Borrower, each of the Subsidiary
Guarantors and the Bank.

                 4.02     New Note.  The Borrower hereby agrees to deliver to
the Bank a new promissory note (the "New Note") duly completed in accordance
with Section 2.05 of the Credit Agreement in extension, renewal and
substitution of the Note previously delivered by the Borrower to the Bank.

                 4.03     Opinion of Counsel.  Delivery of an opinion, dated
the date of this Amendment, of Fulbright & Jaworski LLP, special New York
counsel to the Obligors, substantially in the form of Exhibit A hereto and
covering such other matters as the Bank may reasonably request (and each
Obligor hereby instructs such counsel to deliver such opinions to the Bank).

                 4.04.  Other Documents.  The Bank shall have received such
documents as the Bank or special New York counsel to the Bank may reasonably
request.

                 Section 5.  Miscellaneous.  Except as herein provided, the
Credit Agreement shall remain unchanged and in full force and effect.  This
Amendment No. 1 may be executed in any number of counterparts, all of which
taken together shall constitute one and the same amendatory instrument and any
of the parties hereto may execute this Amendment No. 1 by signing any such
counterpart.  This Amendment No. 1 shall be governed by, and construed in
accordance with, the laws of the State of New York.





                                     -3-
<PAGE>   4
                 IN WITNESS WHEREOF, the parties hereto have caused this
Amendment No. 1 to be duly executed and delivered as of the day and year first
above written.


                                          BORROWER
                                          --------

                                          RUTHERFORD--MORAN OIL CORPORATION


                                          By   /s/ David F. Chavenson     
                                            -----------------------------------
                                                   Title:  Vice President


                                          SUBSIDIARY GUARANTORS
                                          ---------------------

                                          RUTHERFORD--MORAN
                                             EXPLORATION COMPANY


                                          By  /s/  David F. Chavenson        
                                            -----------------------------------
                                                   Title:  Vice President


                                          THAI ROMO HOLDINGS, INC.


                                          By  /s/  David F. Chavenson        
                                            -----------------------------------
                                                   Title:  Vice President


                                          THAI ROMO LIMITED


                                          By  /s/  David F. Chavenson         
                                            -----------------------------------
                                                   Title:  Vice President


                                          THE BANK
                                          --------

                                          THE CHASE MANHATTAN BANK


                                          By  /s/  Martha Fetner              
                                            -----------------------------------
                                                   Title:  Vice President






                                     -4-