Exhibit 12.1
 CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICER PURSUANT TO
EXCHANGE ACT RULES 13a-14(a) AND 15d-14(a)
AS ADOPTED PURSUANT TO SECTION 302
OF THE SARBANES-OXLEY ACT OF 2002
  1.
    
    I have reviewed this annual report on Form 20-F of Petrobras Argentina 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)) and internal control over financial reporting (as defined in Exchange Act
Rules 13a-15(f) and 15d-15(f)) 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)
    
    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 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
 (d)
    
    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 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.
  By:
    /s/ Carlos Alberto da CostaCarlos Alberto da CostaChief Executive Officer