<PAGE>

                                                                   EXHIBIT 10.8

                                  EXHIBIT "C"

                             ASSIGNMENT AND RELEASE

         THIS ASSIGNMENT AND RELEASE ("Assignment") is made by and between
Benton Oil and Gas Company, a Delaware corporation ("Benton") and Benton Oil
and Gas Company (Senegal), Ltd., a corporation registered under the laws of
the Cayman Islands ("Benton Senegal"), Fortesa Corporation, a Texas
corporation ("Fortesa") and First Seismic Corporation, a Delaware corporation
("First").

         In consideration of the mutual promises made between the parties
hereto and other good and valuable consideration, and pursuant to and subject
to the terms of that certain Agreement (the "Agreement") dated October 23, 1999
between the parties hereto, Benton and Benton Senegal hereby:

         BARGAIN, SELL, CONVEY, ASSIGN, TRANSFER AND DELIVER unto Fortesa all
of their rights, title and interest under the following agreements:

         (a)      The Farmout Agreement dated December 17, 1997, by and between
                  the Societe Des Petroles Du Senegal ("Petrosen") and Fortesa
                  and Benton to explore and exploit hydrocarbons and undertake
                  certain work programs in connection with Petrosen's Thies
                  Block in the onshore area of the Republic of Senegal (the
                  "Farmout"), a copy of which is attached hereto as Exhibit A;

         (b)      The Memorandum of Understanding of November 25, 1997, between
                  Benton, Fortesa and Petrosen, a copy of which is attached
                  hereto as Exhibit B;

         (c)      The Memorandum of Understanding dated December 17, 1997,
                  between Fortesa and Benton, a copy of which is attached hereto
                  as Exhibit C;

                                      - 1 -

<PAGE>


         (d)      The Joint Operating Agreement dated January 16, 1998 between
                  Benton Senegal, Fortesa and Petrosen, a copy of which is
                  attached hereto as Exhibit D; and

         (e)      All other documents, agreements or rights related to the
                  Farmout (which shall be deemed to include agreements
                  pertaining to the Thies Block between Benton and/or Benton
                  Senegal and third parties).

The foregoing documents are collectively referred to herein as the "Farmout
Rights."

         THIS ASSIGNMENT shall be subject to the following terms, conditions
and exceptions:

         1. This Assignment shall be effective as of 7:00 a.m., Pacific
Standard Time, on the date of execution hereof.

         2. Fortesa and First hereby relieve and release Benton and Benton
Senegal from any and all obligations, duties and requirements which Benton
and/or Benton Senegal has or might have to Fortesa and/or First pursuant to
the Farmout Rights.

         3. First and Fortesa hereby agree to fully protect, indemnify and
defend Benton and Benton Senegal, their respective officers, agents and/or
employees and hold them harmless from any and all claims, losses, damages,
demands, suits, causes of action and liabilities (including without
limitation reasonable attorney's fees, costs of litigation and/or
investigation and other costs associated therewith) of every kind whatsoever
arising out the Farmout Rights or any part thereof, after the date hereof
regardless of cause or of Benton's and/or Benton Senegal's negligence or
fault, whether imposed by statute, rule or regulation or strict liability as
to Benton and/or Benton Senegal, their respective officers, agents and/or
employees. The indemnity of Benton and/or Benton Senegal provided for herein
is limited to the duties and obligations of Benton and/or Benton Senegal
arising out of the instruments denoted as the Farmout Rights herein and does
not cover or include claims,

                                 - 2 -

<PAGE>

losses (damages, demands, suits, causes of action and liabilities (including
without limitation reasonable attorney's fees, costs of litigation and/or
investigation and other costs associated therewith) arising out of any act or
omission under the laws of the Republic of Senegal and not out of the
foregoing instruments.

         4. The terms, conditions or exceptions contained herein shall
constitute covenants running with the land and shall be binding upon, and for
the benefit of, the respective successors and assigns of Benton, Benton
Senegal, First and Fortesa.

         5. This Assignment does not negate the terms and provisions of the
Agreement and without limitation particularly Section 6.1 thereof.

         6. This Assignment may be executed in any number of counterparts,
and each and every counterpart will be deemed for all purposes one agreement.

         THIS ASSIGNMENT IS MADE WITHOUT WARRANTY OF ANY KIND, EXPRESS,
STATUTORY, OR IMPLIED, AND BENTON AND BENTON SENEGAL ARE TRANSFERRING THE
FARMOUT RIGHTS WITHOUT ANY EXPRESS STATUTORY OR IMPLIED WARRANTY WHATSOEVER
AS TO TITLE, DESCRIPTION, PHYSICAL CONDITION OF THE PROPERTY (INCLUDING
WITHOUT LIMITATION, TO ENVIRONMENTAL CONDITION OF THE PROPERTY), QUALITY,
VALUE, FITNESS FOR PURPOSE, MERCHANTABILITY, OR OTHERWISE EXCEPT AS SET FORTH
HEREIN.

         Benton and Benton Senegal agrees to execute and deliver to Fortesa
all such other additional instruments and other documents and to do all such
other and further acts and things as may be reasonably necessary to more
fully and effectively grant, convey and assign to Fortesa the Farmout Rights.

         IN WITNESS WHEREOF, the parties hereto have caused the Agreement to
be executed this 23 day of October, 1999.

                                    - 3 -

<PAGE>

                                      BENTON OIL AND GAS COMPANY


                                      By: /s/ Andrei E. Popov
                                         -----------------------------------
                                      Name:   Andrei E. Popov
                                           ---------------------------------
                                      Title:  Vice President
                                            --------------------------------


                                      BENTON OIL AND GAS COMPANY (SENEGAL), LTD.


                                      By: /s/ Andrei E. Popov
                                         -----------------------------------

                                      Name:   Andrei E. Popov
                                           ---------------------------------

                                      Title:  Vice President
                                            --------------------------------


                                      FORTESA CORPORATION


                                      By: /s/ [ILLEGIBLE]
                                         -----------------------------------

                                      Name:   [ILLEGIBLE]
                                           ---------------------------------

                                      Title:  Secretary
                                            --------------------------------


                                      FIRST SEISMIC CORPORATION


                                      By: /s/ [ILLEGIBLE]
                                         -----------------------------------

                                      Name:   [ILLEGIBLE]
                                           ---------------------------------

                                      Title:  Vice President
                                            --------------------------------

                                     - 4 -

<PAGE>

STATE OF California

COUNTY OF Santa Barbara

         On this 19th day of November, 1999, before me, the undersigned, a
Notary Public, personally appeared Andrei Popov, personally known to me (or
proved to me on the basis of satisfactory evidence) to be the person whose
name is subscribed to the within instrument and acknowledged to me that he
executed the same in his authorized capacity, and that by his signature on
the instrument Benton Oil and Gas Company executed the instrument.

         WITNESS my hand and official seal.


       /s/ Christina B. Doktor
     -------------------------------------------------
                                                      NOTARY PUBLIC

My Commission Expires:


----------------------                 [SEAL]

                                    - 6 -

<PAGE>

STATE OF California

COUNTY OF Santa Barbara

         On this 19th day of November, 1999, before me, the undersigned, a
Notary Public, personally appeared Andrei Popov, personally known to me (or
proved to me on the basis of satisfactory evidence) to be the person whose
name is subscribed to the within instrument and acknowledged to me that he
executed the same in his authorized capacity, and that by his signature on
the instrument Benton Oil and Gas Company (Senegal), Ltd. executed the
instrument.

         WITNESS my hand and official seal.


       /s/ Christina B. Doktor
     -------------------------------------------------
                                                      NOTARY PUBLIC

My Commission Expires:


----------------------                 [SEAL]


                                     - 7 -

<PAGE>

STATE OF Texas

COUNTY OF Harris


         On this 19th day of November, l999, before me, the undersigned, a
Notary Public, personally appeared Walter H. Walne, III, Secretary,
personally known to me (or proved to me on the basis of satisfactory
evidence) to be the person whose name is subscribed to the within instrument
and acknowledged to me that he executed the same in his authorized capacity,
and that by his signature on the instrument Fortesa Corporation executed the
instrument.

         WITNESS my hand and official seal.


      /s/ Eva J. Hollingsworth
     -------------------------------------------------
                                                      NOTARY PUBLIC

My Commission Expires:


----------------------                 [SEAL]

                                  - 8 -

<PAGE>

STATE OF Texas

COUNTY OF Harris


         On this 19th day of November, l999, before me, the undersigned, a
Notary Public, personally appeared Nicholas E. Rockecharlie, Vice President,
personally known to me (or proved to me on the basis of satisfactory
evidence) to be the person whose name is subscribed to the within instrument
and acknowledged to me that he executed the same in his authorized capacity,
and that by his signature on the instrument First Seismic Corporation,
executed the instrument.

         WITNESS my hand and official seal.


      /s/ Eva J. Hollingsworth
     -------------------------------------------------
                                                      NOTARY PUBLIC

My Commission Expires:


----------------------                 [SEAL]

                                   - 9 -