As filed with the Securities and Exchange Commission on September 12, 2003.
- --------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                   POST EFFECTIVE AMENDMENT NO. 1 TO FORM S-8
             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                                   Nexen INC.
             (Exact name of registrant as specified in its charter)

            CANADA                                      98-6000202
(State or other jurisdiction of               (IRS Employer Identification No.)
incorporation or organization)

                     --------------------------------------

                              801 - 7th Avenue S.W.
                        Calgary, Alberta, Canada T2P 3P7

                        (Address, including zip code, and
                           telephone number, including
                           area code, of registrant's
                               principal executive
                                    offices)


                     Amended and Restated Stock Option Plan
                            (Full title of the plan)

                           Nexen Petroleum U.S.A. Inc.
                                12790 Merit Drive
                                Suite 800, LB 94
                               Dallas, Texas 75251
                     (Name and address of agent for service)



                                 (972) 450-4600
          (Telephone number, including area code, of agent for service)

                             -----------------------


                                   COPIES TO:

                                                         
                 John B. McWilliams                                       Edwin S. Maynard
Senior Vice President, General Counsel and Secretary        Paul, Weiss, Rifkind, Wharton & Garrison LLP
                     Nexen Inc.                                      1285 Avenue of the Americas
                635 - 8th Avenue S.W.                               New York, New York 10019-6064
          Calgary, Alberta, Canada T2P 3Z1




                                                 CALCULATION OF REGISTRATION FEE
===============================================================================================================================
                                                              Proposed Maximum     Proposed Maximum
              Title of                    Amount to be         Offering Price     Aggregate Offering          Amount of
    Securities to be Registered         Registered (1)(2)       Per Share (3)          Price (3)          Registration Fee
- -------------------------------------------------------------------------------------------------------------------------------
                                                                                              
Common Shares, no par value             2,000,000 shares          $ 27.48             $54,960,000            $4,446.27

- -------------------------------------------------------------------------------------------------------------------------------


(1)  This Registration Statement also applies to rights under the Registrant's
     Shareholder Rights Plan Agreement, which are attached to and tradable only
     with the common shares registered hereby. No registration fees are required
     for such rights as they will be issued for no additional consideration.

(2)  This Registration Statement shall, in accordance with Rule 416 under the
     Securities Act of 1933, as amended, be deemed to cover such additional
     shares as may be issued to prevent dilution resulting from stock splits,
     stock dividends or similar transactions.

(3)  Calculated in accordance with Rule 457(c) and (h)(1) under the Securities
     Act as amended, equal to $27.48, the average of the high and low prices
     reported on the New York Stock Exchange on September 8, 2003, a date within
     five business days of the filing of this Registration Statement.





                           INCORPORATION BY REFERENCE
                                       OF
             REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-13574)
             -------------------------------------------------------

                  We are filing this registration statement for the purpose of
registering, in accordance with General Instruction E of Form S-8, an additional
2,000,000 Common Shares, no par value, to be issued under the Registrant's
Amended and Restated Stock Option Plan. We incorporate by reference into this
registration statement on Form S-8 our previously filed registration statement
on Form S-8 (File No. 333-13574, filed on May 31, 2001) in its entirety,
including the exhibits to it.


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT
               --------------------------------------------------

Item 6.  Indemnification of Directors and Officers

                  Section 124 of the Canada Business Corporations Act provides
as follows:

124.     (1)      Indemnification. A corporation may indemnify a director or
                  officer of the corporation, a former director or officer of
                  the corporation or another individual who acts or acted at the
                  corporation's request as a director or officer, or an
                  individual acting in a similar capacity, of another entity,
                  against all costs, charges and expenses, including an amount
                  paid to settle an action or satisfy a judgment, reasonably
                  incurred by the individual in respect of any civil, criminal,
                  administrative, investigative or other proceeding in which the
                  individual is involved because of that association with the
                  corporation or other entity.

         (2)      Advance of Costs. A corporation may advance moneys to a
                  director, officer or other individual for the costs, charges
                  and expenses of a proceeding referred to in subsection (1).
                  The individual shall repay the moneys if the individual does
                  not fulfil the conditions of subsection (3).

         (3)      Limitation. A corporation may not indemnify an individual
                  under subsection (1) unless the individual

                  (a)      acted honestly and in good faith with a view to the
                           best interests of the corporation, or, as the case
                           may be, to the best interests of the other entity for
                           which the individual acted as director or officer or
                           in a similar capacity at the corporation's request;
                           and

                  (b)      in the case of a criminal or administrative action or
                           proceeding that is enforced by a monetary penalty,
                           the individual had reasonable grounds for believing
                           that the individual's conduct was lawful.

         (4)      Indemnification in derivative actions. A corporation may with
                  the approval of a court, indemnify an individual referred to
                  in subsection (1), or advance moneys under subsection (2), in
                  respect of an action by or on behalf of the corporation or
                  other entity to procure a judgment in its favour, to which the
                  individual is made a party because of the individual's
                  association with the corporation or other entity





                  as described in subsection (1) against all costs, charges and
                  expenses reasonably incurred by the individual in connection
                  with such action, if the individual fulfills the conditions
                  set out in subsection (3).

         (5)      Right to indemnity. Despite subsection (1), an individual
                  referred to in that subsection is entitled to indemnity from
                  the corporation in respect of all costs, charges and expenses
                  reasonably incurred by the individual in connection with the
                  defence of any civil, criminal, administrative, investigative
                  or other proceeding to which the individual is subject because
                  of the individual's association with the corporation or other
                  entity as described in subsection (1), if the individual
                  seeking indemnity

                  (a)      was not judged by the court or other competent
                           authority to have committed any fault or omitted to
                           do anything that the individual ought to have done;
                           and

                  (b) fulfills the conditions set out in subsection (3).

         (6)      Insurance. A corporation may purchase and maintain insurance
                  for the benefit of an individual referred to in subsection (1)
                  against any liability incurred by the individual

                  (a)      in the individual's capacity as a director or officer
                           of the corporation; or

                  (b)      in the individual's capacity as a director or
                           officer, or similar capacity, of another entity, if
                           the individual acts or acted in that capacity at the
                           corporation's request.

         (7)      Application to court. A corporation, an individual or an
                  entity referred to in subsection (1) may apply to a court for
                  an order approving an indemnity under this section and the
                  court may so order and make any further order that it sees
                  fit.

         (8)      Notice to Director. An applicant under subsection (7) shall
                  give the Director notice of the application and the Director
                  is entitled to appear and be heard in person or by counsel.

         (9)      Other notice. On an application under subsection (7) the court
                  may order notice to be given to any interested person and the
                  person is entitled to appear and be heard in person or by
                  counsel.



                  Section 7 of the By-laws of the Registrant contains the
following provisions with respect to indemnification of the Registrant's
directors and officers with respect to certain insurance maintained by the
Registrant with respect to its indemnification obligations:





7.01     LIMITATION OF LIABILITY.

         Every director and officer of the Corporation in exercising his powers
         and discharging his duties shall act honestly and in good faith with a
         view to the best interests of the Corporation and shall exercise the
         care, diligence and skill that a reasonable prudent person would
         exercise in comparable circumstances, including reliance in good faith
         on:

                  (a)      financial statements of the Corporation represented
                           to the director by an officer of the Corporation or
                           in a written report of the auditor of the Corporation
                           fairly to reflect the financial condition of the
                           Corporation; or
                  (b)      a report of a person whose profession lends
                           credibility to a statement made by the professional
                           person.

         Subject to the foregoing, no director or officer shall be liable for
         the acts, receipts, neglects or defaults of any other director, officer
         or employee, or for joining in any receipt or other act for conformity,
         or for any loss, damage or expense happening to the Corporation through
         the insufficiency or deficiency of title to any property acquired for
         or on behalf of the Corporation, or for the insufficiency or deficiency
         of any security in or upon which any of the moneys of the Corporation
         shall be invested, or for any loss or damage arising from the
         bankruptcy, insolvency or tortious acts of any person with whom any of
         the moneys, securities or effects of the Corporation shall be
         deposited, or for any loss occasioned by any error of judgement or
         oversight on his part, or for any other loss, damage or misfortune
         which shall happen in the execution of the duties of his office or
         trust or in relation thereto; provided that nothing herein shall
         relieve any director or officer from the duty to act in accordance with
         the Act and the regulations thereunder or from liability for any breach
         thereof.

7.02     INDEMNITY.

         Subject to the provisions of the Act, the Corporation shall indemnify a
         director officer, a former director or officer or another individual
         who acts or acted at the Corporation's request as a director or
         officer, or an individual acting in a similar capacity of another
         entity, against all costs, charges and expenses, including an amount
         paid to settle an action or satisfy a judgement, reasonably incurred by
         the individual in respect to any civil, criminal, administrative or
         investigative action or other proceeding in which the individual is
         involved because of that association with the Corporation or other
         entity if, exercising the care, diligence and skill that a reasonably
         prudent person would exercise in comparable circumstances: (a) the
         individual acted honestly and in good faith with a view to the best
         interests of the Corporation or, as the case may be, to the best
         interests of the other entity for which the individual acted as
         director or officer or in a similar capacity at the Corporation's
         request, and (b) in the case of a criminal or administrative action or
         proceeding that is enforced by a monetary penalty, the individual had
         reasonable grounds for believing that the individual's conduct was
         lawful. The Corporation shall also indemnify any such person in such
         other circumstances as the Act or law permits or requires. Nothing in
         this by-law shall limit the right of any person entitled to indemnity
         to claim indemnity apart from the provisions of this by-law to the
         extent permitted by the Act or law.





7.03     ADVANCE OF COSTS.

         The Corporation may advance moneys to any director, officer or other
         individual for the costs, charges and expenses of a proceeding referred
         to in Section 7.02. The individual, however, shall repay the moneys to
         the Corporation if the individual does not fulfill the conditions set
         out in subsection 7.02(a) and, as applicable, subsection 7.02(b).

7.04     INSURANCE.

         Subject to the Act, the Corporation may purchase and maintain insurance
         for the benefit of any person referred to in Section 7.02 against any
         liability incurred by him in his capacity as a director or officer of
         the Corporation or of another body corporate where he acts or acted in
         that capacity at the Corporation's request.


Item 8. Exhibits

EXHIBIT        DESCRIPTION
- -------        -----------

4.1            By-Law No. 1 of the Registrant enacted February 15, 2002, being a
               by-law relating generally to the transaction of the business and
               affairs of the Registrant (filed as Exhibit 2 to Form 8A/A dated
               August 20, 2002, filed by the Registrant and incorporated by
               reference herein)

4.2            Amended and Restated Shareholder Rights Plan Agreement dated May
               2, 2002 between the Corporation and CIBC Mellon Trust Company, as
               Rights Agent, which includes the Form of Rights Certificate as
               Exhibit A (filed as Exhibit 3 to Form 8-A/A dated August 20,
               2002, filed by the Registrant and incorporated by reference
               herein)

5.1            Opinion of Blake, Cassels & Graydon LLP, counsel to Nexen, Inc.,
               regarding the legality of the securities being registered

23.1           Consent of Blake, Cassels & Graydon LLP, counsel to Nexen Inc.

23.2           Consent of Deloitte & Touche LLP

24.1           Powers of Attorney (included on the signature pages to this
               registration statement)






                                   SIGNATURES

                  Pursuant to the requirements of the Securities Act of 1933,
the registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
registration statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Calgary, Province of Alberta, on September 12,
2003.

                                           NEXEN INC.


                                           By: /s/ John B. Mcwilliams
                                               -------------------------------
                                               John B. McWilliams
                                               Senior Vice President, General
                                               Counsel and Secretary


                  KNOW ALL PERSONS BY THESE PRESENTS, that each person whose
signature appears below constitutes and appoints John B. McWilliams and Charles
W. Fischer as such person's true and lawful attorneys-in-fact and agents, with
full power of substitution and revocation, for such person and in such person's
name, place and stead, in any and all capacities (until revoked in writing), to
sign any and all amendments (including post-effective amendments) to this
registration statement and to file the same with all exhibits thereto, and the
other documents in connection therewith, with the Securities and Exchange
Commission, granting unto said attorneys-in-fact and agents, and each of them,
full power and authority to do and perform each and every act and things
requisite and necessary to be done, as fully to all intents and purposes as such
person might or could do in person, hereby ratifying and confirming all that
said attorneys-in-fact and agents, or any of them, or their or his substitute or
substitutes, may lawfully do or cause to be done by virtue hereof.

                  Pursuant to the requirements of the Securities Act of 1933,
this Registration Statement has been signed by the following persons in the
capacities indicated effective September 12, 2003:

                SIGNATURE                                 TITLE
                ---------                                 -----


                   *                      President, Chief Executive Officer and
- --------------------------------------    Director (Principal Executive Officer)
           Charles W. Fischer



         /s/ Dennis G. Flanagan           Director
- --------------------------------------
           Dennis G. Flanagan





                SIGNATURE                                 TITLE
                ---------                                 -----


         /s/ David A. Hentschel           Director
- --------------------------------------
           David A. Hentschel



          /s/ S. Barry Jackson            Director
- --------------------------------------
            S. Barry Jackson



          /s/ Kevin J. Jenkins            Director
- --------------------------------------
            Kevin J. Jenkins



          /s/ Thomas C. O'neill           Director
- --------------------------------------
            Thomas C. O'Neill



         /s/ Francis M. Saville           Director
- --------------------------------------
           Francis M. Saville



         /s/ Richard M. Thomson           Director
- --------------------------------------
           Richard M. Thomson



           /s/ John M. Willson            Director
- --------------------------------------
             John M. Willson



         /s/ Victor J. Zaleschuk          Director
- --------------------------------------
           Victor J. Zaleschuk



          /s/ Marvin F. Romanow           Executive Vice President and Chief
- --------------------------------------    Financial Officer (Principal Financial
            Marvin F. Romanow             Officer)





                SIGNATURE                                 TITLE
                ---------                                 -----


          /s/ Michael J. Harris           Controller
- --------------------------------------    (Controller and Principal Accounting
            Michael J. Harris             Officer)



* executed pursuant to power-of-
  attorney filed previously.


Pursuant to the requirements to Section 6(a) of the Securities Act, the
undersigned has signed this Registration Statement solely in the capacity of the
duly authorized representative of the Registrant in the United States on
September 12, 2003.


                                     NEXEN PETROLEUM U.S.A. INC.



                                     By: /s/ Douglas B. Otten
                                         -------------------------------------
                                         Douglas B. Otten
                                         President and Chairman of the Board






                                  EXHIBIT INDEX
                                  -------------


EXHIBIT        DESCRIPTION
- -------        -----------

4.1            By-Law No. 1 of the Registrant enacted February 15, 2002, being a
               by-law relating generally to the transaction of the business and
               affairs of the Registrant (filed as Exhibit 2 to Form 8A/A dated
               August 20, 2002, filed by the Registrant and incorporated by
               reference herein)

4.2            Amended and Restated Shareholder Rights Plan Agreement dated May
               2, 2002 between the Corporation and CIBC Mellon Trust Company, as
               Rights Agent, which includes the Form of Rights Certificate as
               Exhibit A (filed as Exhibit 3 to Form 8-A/A dated August 20,
               2002, filed by the Registrant and incorporated by reference
               herein)

5.1            Opinion of Blake, Cassels & Graydon LLP, counsel to Nexen, Inc.,
               regarding the legality of the securities being registered

23.1           Consent of Blake, Cassels & Graydon LLP, counsel to Nexen Inc.

23.2           Consent of Deloitte & Touche LLP

24.1           Powers of Attorney (included on the signature pages to this
               registration statement)