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                                                                    EXHIBIT 32.1
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CERTIFICATION OF PERIODIC REPORT

I, Marvin F.  Romanow,  President and Chief  Executive  Officer of Nexen Inc., a
Canadian Corporation (the "Company") certify, pursuant to 18 U.S.C. Section 1350
as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

(1)    the Quarterly Report on Form 10-Q of the Company for the quarterly period
       ended  September  30,  2009 as filed  with the  Securities  and  Exchange
       Commission  on the date hereof (the  "Report")  fully  complies  with the
       requirements of Section 13(a) or 15(d) of the Securities  Exchange Act of
       1934 (15 U.S.C. 78m or 78o(d)); and

(2)    the information  contained in the Report fairly presents, in all material
       respects,  the  financial  condition  and  results of  operations  of the
       Company.



Date:  November 3, 2009

                                        /s/ Marvin F. Romanow
                                        ---------------------
                                        Marvin F. Romanow
                                        President and Chief Executive Officer


A signed  original of this  written  statement  required by Section 906 has been
provided to Nexen Inc. and shall be retained by Nexen Inc. and  furnished to the
Securities and Exchange Commission or its staff upon request.