EXHIBIT 31.1
CERTIFICATIONS

I, Marvin F. Romanow, certify that:

1.      I have reviewed this quarterly report on Form 10-Q of Nexen Inc.

2.      Based on my knowledge, this report does not contain any untrue statement
        of a material  fact or omit to state a material  fact  necessary to make
        the  statements  made,  in light of the  circumstances  under which such
        statements  were made, not misleading with respect to the period covered
        by this report;

3.      Based on my knowledge,  the financial  statements,  and other  financial
        information  included in this  report,  fairly  present in all  material
        respects the financial  condition,  results of operations and cash flows
        of the registrant as of, and for, the periods presented in this report;

4.      The  registrant's  other  certifying  officer and I are  responsible for
        establishing  and  maintaining  disclosure  controls and  procedures (as
        defined in exchange  Act Rules  13a-15(e)  and  15d-15(e))  and internal
        control  over  financial  reporting  (as defined in  Exchange  Act Rules
        13a-15(f) and 15d-15(f)) for the registrant and we have:

        (a)     designed such disclosure controls and procedures, or caused such
                disclosure  controls  and  procedures  to be designed  under our
                supervision, to ensure that material information relating to the
                registrant,  including its  consolidated  subsidiaries,  is made
                known to us by others within those entities, particularly during
                the period in which this report is being prepared;

        (b)     designed  such internal  control over  financial  reporting,  or
                caused such  internal  control  over  financial  reporting to be
                designed under our supervision,  to provide reasonable assurance
                regarding  the  reliability  of  financial   reporting  and  the
                preparation  of financial  statements  for external  purposes in
                accordance with generally accepted accounting principles;

        (c)     evaluated  the  effectiveness  of  the  registrant's  disclosure
                controls  and  procedures  and  presented  in  this  report  our
                conclusions about the  effectiveness of the disclosure  controls
                and  procedures,  as of the end of the  period  covered  by this
                report based on such evaluation; and

        (d)     disclosed in this report any change in the registrant's internal
                control  over  financial  reporting  that  occurred  during  the
                registrant's most recent fiscal quarter (the registrant's fourth
                fiscal  quarter  in the  case  of an  annual  report)  that  has
                materially  affected,  or is  reasonably  likely  to  materially
                affect,   the  registrant's   internal  control  over  financial
                reporting; and

5.      The registrant's other certifying officer and I have disclosed, based on
        our most recent evaluation of internal control over financial reporting,
        to the registrant's auditors and the audit committee of the registrant's
        board of directors (or persons performing the equivalent function):

        (a)     all  significant  deficiencies  and material  weaknesses  in the
                design or operation of internal control over financial reporting
                which are reasonably likely to adversely affect the registrant's
                ability  to record,  process,  summarize  and  report  financial
                information; and

        (b)     any fraud, whether or not material,  that involves management or
                other employees who have a significant  role in the registrant's
                internal control over financial reporting.



        Date: July 21, 2010

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


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