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                                  EXHIBIT 32.1
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 June 30, 2010 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: July 21, 2010

                                           /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.


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