EXHIBIT 99.1 Certificate Pursuant to Section 1350 of Chapter 63 of Title 18 of the United States Code The undersigned officers hereby certify, as to the Quarterly Report on Form 10-Q of CITGO Petroleum Corporation for the quarterly period ended June 30, 2002, that (i) the report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, and (ii) the information contained in the report fairly presents, in all material respects, the financial condition and results of operations of CITGO Petroleum Corporation and its subsidiaries. Date: August 9, 2002 /s/ Oswaldo Contreras ------------------------------------------ Oswaldo Contreras Chief Executive Officer CITGO Petroleum Corporation Date: August 9, 2002 /s/ Eddie R. Humphrey ------------------------------------------ Eddie R. Humphrey Chief Financial Officer CITGO Petroleum Corporation