EXHIBIT 99.1 CERTIFICATION WITH RESPECT TO QUARTERLY REPORT OF NUEVO ENERGY COMPANY The undersigned, being the chief executive officer and chief financial officer of Nuevo Energy Company (the "Company"), in compliance with 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, do hereby certify with respect to the Quarterly Report of the Company on Form 10-Q, as filed with the Securities and Exchange Commission on August [14], 2002 (the "Report"): 1. that the Report fully complies with all requirements of Section 13(a) and 15(d) of the Securities Exchange Act of 1934; and 2. that the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company. Date: August 14, 2002 By: /s/ James L. Payne --------------------------- -------------------------------- James L. Payne Chairman, President and Chief Executive Officer Date: August 14, 2002 By: /s/ Janet F. Clark --------------------------- -------------------------------- Janet F. Clark Senior Vice President and Chief Financial Officer