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                                                                    Exhibit 12.1


                                  Certification

I, Alberto Guimaraes, certify that:


   1. I have reviewed this annual report on Form 20-F of Petrobras Energia
      Participaciones S.A.;


   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 company as of, and for, the periods presented in this report;


   4. The company'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-15(e)) for the company 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
            company, 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 company'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 company'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 company's internal
            control over financial reporting; and


   5. The company's other certifying officer(s) and I have disclosed, based on
      our most recent evaluation of internal control over financial reporting,
      to the company's auditors and the audit committee of the company'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 company'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 company's
            internal control over financial reporting.


Date: July 8, 2004

                                       /s/ Alberto Guimaraes
                                       -----------------------------------------
                                       Alberto Guimaraes
                                       Chief Executive Officer