EXHIBIT 10.5a

                      FIRST AMENDMENT TO CREDIT AGREEMENT

      This First  Amendment to Credit  Agreement  (this "First  Amendment")  is
effective as of January 7,  2003 (the "Effective  Date"),  by and among WHITING
PETROLEUM  CORPORATION,  a Delaware corporation  ("Borrower"),  BANK ONE, NA, a
national  banking  association,   as  Administrative  Agent  ("Administrative
Agent"),  and each of the financial  institutions  a party hereto  (hereinafter
collectively referred to as "Banks", and individually, "Bank").

                             W I T N E S S E T H:
                             --------------------

      WHEREAS,  Borrower,  Administrative  Agent and Banks are  parties to that
certain  Credit  Agreement  dated  as  of  December 20,   2002  (the  "Credit
Agreement")  (unless otherwise defined herein, all terms used herein with their
initial  letter  capitalized  shall  have the  meaning  given such terms in the
Credit Agreement); and

      WHEREAS,  pursuant  to the Credit  Agreement,  Banks have made  revolving
credit loans to Borrower; and

      WHEREAS,  Borrower has requested that the Credit  Agreement be amended in
certain respects; and

      WHEREAS,  subject to the terms and  conditions  set forth  herein,  Banks
have agreed to Borrower's request.

      NOW  THEREFORE,  for and in  consideration  of the mutual  covenants  and
agreements  herein  contained  and other good and valuable  consideration,  the
receipt  and  sufficiency  of which  are  hereby  acknowledged  and  confessed,
Borrower, Administrative Agent and Banks hereby agree as follows:

SECTION 1. Amendments.   In  reliance  on  the   representations,   warranties,
covenants  and  agreements  contained  in  this  First  Amendment,  the  Credit
Agreement is hereby  amended  effective as of the Effective  Date in the manner
provided in this Section 1.

1.1.  Amendment  to  Definition  of "Loan  Papers".  The  definition  of "Loan
Papers"  contained in Section 1.1 of the Credit  Agreement  shall be amended to
read in full as follows:

           "Loan Papers" means this Agreement,  the First Amendment, the Notes,
      each  Facility  Guaranty  which may now or hereafter  be  executed,  each
      Borrower Pledge  Agreement  which may now or hereafter be executed,  each
      Subsidiary  Pledge Agreement which may now or hereafter be executed,  all
      Mortgages   now  or  at  any  time   hereafter   delivered   pursuant  to
      Section 5.1,   all  Letters  of  Credit,  and  all  other   certificates,
      documents or instruments delivered in connection with this Agreement,  as
      the foregoing may be amended from time to time.

1.2.  Additional  Definition.  Section 1.1  of the  Credit  Agreement  shall be
amended to add the following definition of "First Amendment" to such Section:

           "First  Amendment"  means that  certain  First  Amendment  to Credit
      Agreement dated as of January 7,  2003,  among  Borrower,  Administrative
      Agent and Banks.

1.3.  Amendment to  Section 2.1(b).  The fourth sentence of the first paragraph
of Section 2.1(b) shall be amended to read in its entirety as follows:

           "No Letter of Credit  shall have an  expiration  date later than the
      earlier of (i) one (1)  year after the Termination  Date, or (ii) fifteen
      (15) months from the date of issuance  (or, in the case of any renewal or
      extension thereof, fifteen (15) months after such renewal or extension)."

<PAGE>

SECTION 2. Representations  and  Warranties  of  Borrower.  To induce Banks and
Administrative  Agent to enter  into  this  First  Amendment,  Borrower  hereby
represents and warrants to Banks and Administrative Agent as follows:

2.1.  Due Authorization;  No Conflict. The execution,  delivery and performance
by Borrower of this First  Amendment are within  Borrower's  corporate  powers,
have been duly authorized by all necessary  action,  require no action by or in
respect of, or filing with, any  governmental  body,  agency or official and do
not violate or constitute a default  under any  provision of applicable  law or
any  Material  Agreement  binding  upon  Borrower or result in the  creation or
imposition  of any Lien upon any of the  assets of  Borrower  except  Permitted
Encumbrances.

2.2.  Validity and Enforceability.  This First Amendment  constitutes the valid
and binding  obligation of Borrower  enforceable in accordance  with its terms,
except  as (i)  the  enforceability  thereof  may  be  limited  by  bankruptcy,
insolvency or similar laws  affecting  creditor's  rights  generally,  and (ii)
the availability of equitable  remedies may be limited by equitable  principles
of general application.

SECTION 3. Miscellaneous.

3.1.  Reaffirmation  of Loan  Papers.  Any and all of the terms and  provisions
of the Credit  Agreement  and the Loan  Papers  shall,  except as  amended  and
modified   hereby,   remain  in  full   force  and   effect.   The   amendments
contemplated   hereby  shall  not  limit  or  impair  any  Liens  securing  the
Obligations,  each of which are  hereby  ratified,  affirmed  and  extended  to
secure the Obligations.

3.2.  Parties  in  Interest.  All of the terms  and  provisions  of this  First
Amendment  shall bind and inure to the benefit of the parties  hereto and their
respective successors and assigns.

3.3.  Legal  Expenses.  Borrower  hereby agrees to pay on demand all reasonable
fees  and   expenses   of  counsel  to   Administrative   Agent   incurred   by
Administrative  Agent in  connection  with  the  preparation,  negotiation  and
execution of this First Amendment.

3.4.  Counterparts.  This First Amendment may be executed in counterparts,  and
all parties need not execute the same counterpart;  however,  no party shall be
bound by this First  Amendment  until all parties have executed a  counterpart.
Facsimiles shall be effective as originals.

3.5.  Complete  Agreement.  THIS FIRST AMENDMENT,  THE CREDIT AGREEMENT AND THE
OTHER LOAN PAPERS  REPRESENT THE FINAL  AGREEMENT AMONG THE PARTIES AND MAY NOT
BE  CONTRADICTED  BY EVIDENCE OF PRIOR,  CONTEMPORANEOUS  OR ORAL AGREEMENTS OF
THE  PARTIES.  THERE ARE NO  UNWRITTEN  ORAL  AGREEMENTS  BETWEEN  OR AMONG THE
PARTIES.

3.6.  Headings.  The  headings,  captions and  arrangements  used in this First
Amendment are, unless specified  otherwise,  for convenience only and shall not
be deemed to limit,  amplify or modify the terms of this First  Amendment,  nor
affect the meaning thereof.

3.7.  Effectiveness.  This First  Amendment  shall be  effective  automatically
and without necessity of any further action by Borrower,  Administrative  Agent
or  Banks  when   counterparts   hereof  have  been   executed   by   Borrower,
Administrative  Agent and all Banks,  and all  conditions to the  effectiveness
hereof set forth herein have been satisfied.

      IN WITNESS  WHEREOF,  the parties hereto have caused this First Amendment
to be duly  executed by their  respective  Authorized  Officers on the date and
year first above written.

                          [Signature pages to follow]

<PAGE>

                               SIGNATURE PAGE TO
                      FIRST AMENDMENT TO CREDIT AGREEMENT
                                 BY AND AMONG
                  WHITING PETROLEUM CORPORATION, AS BORROWER,
                     BANK ONE, NA, AS ADMINISTRATIVE AGENT
                          AND THE BANKS PARTY THERETO


                               BORROWER:

                               WHITING PETROLEUM CORPORATION, a Delaware
                               corporation

                               By: /s/ James J. Volker
                                   -----------------------
                               Name: James J. Volker
                                     ---------------------
                               Title: CEO
                                      --------------------





<PAGE>

                               SIGNATURE PAGE TO
                      FIRST AMENDMENT TO CREDIT AGREEMENT
                                 BY AND AMONG
                  WHITING PETROLEUM CORPORATION, AS BORROWER,
                     BANK ONE, NA, AS ADMINISTRATIVE AGENT
                          AND THE BANKS PARTY THERETO


                               ADMINISTRATIVE AGENT:

                               BANK ONE, NA



                               /s/ J. Scott Fowler
                               -------------------
                               J. Scott Fowler,
                               Director, Capital Markets



                               BANKS:

                               BANK ONE, NA



                               /s/ J. Scott Fowler
                               -------------------
                               J. Scott Fowler,
                               Director, Capital Markets

                               WACHOVIA BANK, NATIONAL ASSOCIATION


                               By: /s/ Philip Trinder
                                   ----------------------
                               Name: Philip Trinder
                                     --------------------
                               Title: Vice President
                                      -------------------