EXHIBIT 31.1
                                                                    ------------


CERTIFICATIONS

I, Charles W. Fischer, President and Chief Executive Officer, certify that:

1.   I have reviewed the Annual Report on Form 10-K of Nexen, Inc. for the year
     ended December 31, 2003 as filed with the Securities and Exchange
     Commission on February 20, 2004, as amended by Amendment No.1 (as amended
     to date, the "Report");

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(s) and I are responsible for
     establishing and maintaining disclosure controls and procedures (as defined
     in Exchange Act Rules 13a-15(e) and 15d-1(e)) 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)  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

     (c)  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 likely to materially affect, the registrant's
          internal control over financial reporting; and;

5.   The registrant's other certifying officer(s) 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 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: March 1, 2005                                       /s/ Charles W. Fischer
                                                          ----------------------
                                                              Charles W. Fischer
                                          President, and Chief Executive Officer