EXHIBIT 31.1
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CERTIFICATIONS

I, Charles W. Fischer, 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 12, 2007                     /s/ Charles W. Fischer
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                                         Charles W. Fischer
                                         President and Chief Executive Officer