Exhibit
        99.3
 **CERTIFICATION
        PURSUANT TO SECTION 302 OF SARBANES-OXLEY ACT**
  
 I,
        Ronald
        A. Brenneman, certify that:
 
 1.  I
        have
        reviewed this annual report on Form 40-F of Petro-Canada;
 
 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 issuer as of, and
        for, the periods presented in this report;
 
 4.  The
        issuer'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)) for the issuer and 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 issuer, 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 issuer'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 issuer's internal control over financial
        reporting that occurred during the period covered by the annual report that
        has  materially affected, or is reasonably likely to materially affect, the
        issuer's internal control over financial reporting; and
 
 5.  The
        issuer's other certifying officer and I have disclosed, based on our most
        recent
        evaluation of internal control over financial reporting, to the issuer's
        auditors and the audit committee of the issuer's board of directors (or persons
        performing the equivalent functions):
 
 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 issuer'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 issuer's control over financial reporting.
 
 Date:
                  March 23, 2006
              /s/
                  Ronald A. BrennemanRonald
                  A. BrennemanPresident
                  and Chief Executive
                  Officer