FILED PURSUANT TO RULE 424(B)(3)
                                                     REGISTRATION NO. 333-110451
                                                                   333-110451-01

PROSPECTUS SUPPLEMENT NO. 6

                                  $125,000,000
                                GATX CORPORATION
                      5% SENIOR CONVERTIBLE NOTES DUE 2023
                     FULLY AND UNCONDITIONALLY GUARANTEED BY
                           GATX FINANCIAL CORPORATION
                           AND SHARES OF COMMON STOCK
                      ISSUABLE UPON CONVERSION OF THE NOTES

         This prospectus supplement supplements the prospectus dated January 20,
2004 of GATX Corporation and GATX Financial Corporation, as supplemented by
prospectus supplement No. 1 dated January 30, 2004, prospectus supplement No. 2
dated March 15, 2004, prospectus supplement no. 3 dated April 16, 2004,
prospectus supplement no. 4 dated June 2, 2004 and prospectus supplement no. 5
dated October 6, 2004, relating to the sale by certain holders of our 5% Senior
Convertible Notes due 2023 and the shares of our common stock issuable upon
conversion of the notes. You should read this prospectus supplement in
conjunction with the prospectus. This prospectus supplement is qualified by
reference to the prospectus except to the extent that the information in this
prospectus supplement supersedes the information contained in the prospectus.
Capitalized terms used in this prospectus supplement and not otherwise defined
herein have the meanings specified in the prospectus.


         The following line items are hereby added to the table of Selling
Holders contained in the prospectus:


                                                                     PRINCIPAL AMOUNT OF
                                                                     NOTES BENEFICIALLY        NUMBER OF SHARES
                                                                         OWNED THAT            OF COMMON STOCK
NAME OF SELLING HOLDER                                                   MAY BE SOLD           THAT MAY BE SOLD
----------------------                                                   -----------           ----------------
                                                                                         
Standard Pacific Capital Offshore Fund, Ltd.....................            25,000                   1,055

         INVESTING IN THE NOTES AND OUR COMMON STOCK INVOLVES RISKS. SEE "RISK
FACTORS" BEGINNING ON PAGE 5 OF THE PROSPECTUS.

                               -----------------

         NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

                               -----------------




           The date of this prospectus supplement is November 23, 2004