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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 March 31, 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: April 30, 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.