EXHIBIT 99B

                        GATX CORPORATION AND SUBSIDIARIES

                CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350

    CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT TO
                 SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002



In connection with the annual report of GATX Corporation (the "Company") on Form
10-K for the period ending December 31, 2002, as filed with the Securities and
Exchange Commission on the date hereof (the "Report"), I, Ronald H. Zech,
Chairman of the Board and Chief Executive Officer of the Company, certify,
pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, that to my knowledge:

1)       The Report fully complies with the requirements of section 13(a) or
         15(d) of the Securities Exchange Act of 1934; and

2)       The information contained in the Report fairly presents, in all
         material respects, the financial condition and results of operations of
         the Company.




/s/ Ronald H. Zech
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Ronald H. Zech
Chairman and Chief Executive Officer



March 19, 2003