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                                                                    EXHIBIT 10.6

                               FIRST AMENDMENT TO

                          WHITING PETROLEUM CORPORATION

                          PRODUCTION PARTICIPATION PLAN

                                    RECITALS

                1.      Effective January 1, 1981, Whiting Petroleum
Corporation, a Delaware corporation (the "Company") established the Whiting
Petroleum Corporation Production Participation Plan (the "Plan").

                2.      Under section 6.3 of the Plan, the Company reserved to
itself, through action of its board of directors, the right to amend the Plan
from time to time. Pursuant to that power, the Plan is hereby amended, effective
as of October 1, 1983, in the manner set forth below.

                                    AMENDMENT

                1.      The second sentence of Section 6.1 of the Plan is hereby
amended in its entirety to provide as follows:

                "Upon the termination of the Plan, or upon the sale or exchange
        of all or substantially all of the Company's assets, the merger of the
        Company or the liquidation of the Company (but only if the management of
        the purchaser, exchangor or other successor organization is
        substantially different from the management of the Company prior to such
        sale, exchange, merger or liquidation), the interests of all
        participants in the Plan shall become fully vested, notwithstanding any
        other provision hereof."

                IN WITNESS WHEREOF, the undersigned have executed this First
Amendment this 2nd day of December, 1983.

ATTEST:                                  WHITING PETROLEUM CORPORATION

/s/ Patricia J. Butler                   By:  /s/ Kenneth R. Whiting
-------------------------------               -------------------------------<PAGE>

                                                                    EXHIBIT 10.7

                               SECOND AMENDMENT TO

                          WHITING PETROLEUM CORPORATION

                          PRODUCTION PARTICIPATION PLAN

                                    RECITALS

        1.      Effective January 1, 1981, Whiting Petroleum Corporation, a
Delaware corporation (the "Company") established the Whiting Petroleum
Corporation Production Participation Plan (the "Plan").

        2.      Under date of December 2, 1983, a first amendment to the Plan
was adopted.

        3.      Under section 6.3 of the Plan, the Company reserved to itself,
through action of its board of directors, the right to amend the Plan from time
to time. Pursuant to that power, the Plan is hereby amended, effective as of
January 1, 1989, in the manner set forth below.

                                    AMENDMENT

        1.      The figure two percent (2%) of 8/8ths where the same appears in
sub-paragraphs (i) and (ii) of Section 3.1(a) of Article III is hereby changed
to read three percent (3%).

        IN WITNESS WHEREOF, the undersigned have executed this Second Amendment
this ninth day of November 1989.

                                          WHITING PETROLEUM CORPORATION
ATTEST:

/s/ Patricia J. Byberg                    By:  /s/ Kenneth R. Whiting
-----------------------------                  --------------------------------
 Secretary                                      President<PAGE>

                                                                    EXHIBIT 10.8

                               THIRD AMENDMENT TO
                          WHITING PETROLEUM CORPORATION
                          PRODUCTION PARTICIPATION PLAN

                This Third Amendment to the WHITING PETROLEUM CORPORATION
PRODUCTION PARTICIPATION PLAN (the "Plan") is entered into this 30th day of
December, 1997.

                WHEREAS, Whiting Petroleum Corporation (the "Company") is
sponsoring the Whiting Petroleum Corporation Production Participation Plan (the
"Plan") which became effective January 1, 1981; and

                WHEREAS, the Company has amended the Plan by a First Amendment
dated December 2, 1983 and a Second Amendment dated November 9, 1989; and

                WHEREAS, under the Plan the Company reserves to itself, through
action of its Board of Directors, the right to amend the Plan from time to time;
and

                WHEREAS, the Company desires to amend the Plan in the manner set
forth in this Third Amendment.

                NOW, THEREFORE, the Plan is hereby amended effective January 1,
1997 as follows:

                1.      The first sentence of Section 4.6 of the Plan is hereby
amended to read as follows:

                The Company may, at its sole option, purchase the entire vested
        interest under the Plan of any terminated or deceased Participant.

                2.      Except as expressly amended by this Third Amendment, the
Plan shall remain in full force and effect.

                IN WITNESS WHEREOF, this Third Amendment has been executed as of
the day and year first above written.

                                                COMPANY:

                                                WHITING PETROLEUM CORPORATION

                                                /s/  David A. Frawley
                                                -------------------------------<PAGE>

                                                                    EXHIBIT 10.9

                                FOURTH AMENDMENT
                                       TO
                          WHITING PETROLEUM CORPORATION
                          PRODUCTION PARTICIPATION PLAN

                                    RECITALS

        1.      Effective January 1, 1981, Whiting Petroleum Corporation, a
Delaware corporation (the "Company"), established the Whiting Petroleum
Corporation Production Participation Plan (the "Plan").

        2.      Under Section 6.3 of the Plan, the Company reserved to itself,
through action of its Board of Directors, the right to amend the Plan from time
to time. Pursuant to that power, the Plan is hereby amended, effective as of
January 1, 1995, in the manner set forth below:

                                    AMENDMENT

        1.      Article III of the Plan is hereby amended in its entirety to
provide as follows:

                3.1     Allocation of Income Attributable to Pools Formed Prior
        to January 1, 1995. For periods prior to January 1, 1995, the Company
        allocated on its books, for Plan purposes, certain deemed overriding
        royalty interests with respect to certain specified oil and gas
        properties. Interests in wells allocated to the Plan which were either
        spudded or purchased during each Plan Year prior to January 1, 1995 form
        separate accounting pools (the "Pre-1995 Pools"). The calculation of
        income allocable to the Plan and the Participants in the Plan with
        respect to the Pre-1995 Pools, and the distributions to Participants of
        such income, shall continue to be made in accordance with the provisions
        of the Plan as in effect prior to the effective date of this Amendment.

                3.2     Allocation of Income to the Plan for the 1995 Plan Year
        and Subsequent Plan Years. Effective as of January 1, 1995, the Company
        shall allocate to the Plan a specified percentage of the net income with
        respect to the oil and gas wells allocated to the Plan which were either
        spudded or purchased during each Plan Year, beginning with the calendar
        1995 Plan Year. The Company shall determine in its discretion, each Plan
        Year, the wells that shall be allocated to the Plan and the wells that
        are allocated to the Plan during each Plan Year shall form a separate
        accounting pool (the "Post-1994 Pools"). The Pre-1995 Pools and the
        Post-1994 Pools are hereinafter sometimes referred to, in the aggregate,
        as the "Pools". The amount of income that shall be allocated to the Plan
        each Plan Year with respect to each Pool formed in 1995 and later Plan
        Years shall be based upon the net income each Plan Year attributable to
        the oil and gas properties allocated to each such Pool. The amount of
        income allocable to the Plan each Plan Year from each Post-1994 Pool
        shall be based upon the net income attributable to each such Pool's oil
        and gas properties, multiplied by a percentage derived from a sliding
        scale schedule based upon the Company's

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        overall earnings, before interest expense and income taxes, for each
        such Plan Year. The Company shall establish a schedule with respect to
        each Plan Year beginning with the 1995 Plan Year pursuant to which the
        percentage of net property level income that shall be allocated to the
        Plan from all Post-1994 Pools with respect to each such Plan Year shall
        be determined. The applicable percentages for 1995 are attached hereto
        as Exhibit A. For each Plan Year subsequent to 1995, the Company shall
        prepare and approve, as a new Exhibit A, a new schedule establishing the
        levels of contribution to the Plan based upon the Company's earnings
        before interest expense and taxes for such Plan Year. The applicable
        percentage of property-level net income for each Plan Year attributable
        to each Post-1994 Pool shall be distributed annually in accordance with
        Article IV.

                3.3     Sale of Interest. If the Company sells or transfers its
        interest in a well (including the spacing unit on which such well is
        located) that is being used to determine the amount of Plan income
        pursuant to Section 3.1 or 3.2, that portion of the net profit from such
        sale, but before income taxes, representing in the case of Pre-1995
        Pools, the production interest allocated to the Plan, and in the case of
        Post-1994 Pools, the Production Plan Percentage as set forth on Exhibit
        A for the Plan Year during which such sale is closed, shall be
        distributable to the Participants eligible to share in income
        distributions from the Pool in question in the same manner as current
        income from production with respect to that Pool for the Plan Year
        during which such sale occurs.

        IN WITNESS WHEREOF, the undersigned have executed this Second Amendment
this 22nd day of March, 1995.

                                           WHITING PETROLEUM CORPORATION

                                           By:  /s/ Jerry D. Fitzgerald
                                               ---------------------------------
                                               Title: Vice President - Finance

ATTEST:

/s/ Patricia J. Byberg
--------------------------------

                                      - 2 -

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                                    EXHIBIT A
                                       TO
                          WHITING PETROLEUM CORPORATION
                          PRODUCTION PARTICIPATION PLAN

         Schedule of Production Participation Plan Allocations for 1995

               Earnings before                   Production Plan
          Interest Expense and Taxes                Percentage
          --------------------------             ---------------
          11,100,000 or above                          5.0%
          10,600,000 to 11,100,000                     4.7%
          10,100,000 to 10,600,000                     4.4%
          9,600,000 to 10,100,000                      4.1%
          9,100,000 to 9,600,000                       3.8%
          8,900,000 to 9,100,000                       3.5%
          8,400,000 to 8,900,000                       3.2%
          7,900,000 to 8,400,000                       2.9%
          7,400,000 to 7,900,000                       2.6%
          6,900,000 to 7,400,000                       2.3%
          6,900,000 and below                          2.0%

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