EXHIBIT 4.21


                                                                [EXECUTION COPY]


                                  EXTENSION OF
                         SCHEDULED LIQUIDITY COMMITMENT
                                TERMINATION DATE

                  THIS AGREEMENT (this  "Agreement"),  dated as of March 4, 1999
is entered into among Dollar Thrifty  Funding Corp.  ("DTFC"),  the  undersigned
financial  institutions  (the  "Liquidity  Lenders"),  and Credit  Suisse  First
Boston, as Liquidity Agent.


                              W I T N E S S E T H:

         WHEREAS,   the  undersigned  are  parties  to  that  certain  Liquidity
Agreement dated as of March 4, 1998 (the "Liquidity  Agreement") among DTFC, the
Liquidity Lenders, Credit Suisse First Boston, as Liquidity Agent, and The Chase
Manhattan Bank, not as a party but as Syndication Agent;

         WHEREAS,  the  undersigned  desire to extend  the  Scheduled  Liquidity
Commitment Termination Date from March 4, 1999 to March 2, 2000;

         NOW, THEREFORE, the parties hereto hereby agree as follows:

     Section 1. Definitions. Capitalized terms used but not defined herein shall
have the  meanings  assigned to such terms in the  Definitions  List dated as of
March  4,  1998  and  annexed  to the  Liquidity  Agreement  as Annex A, as such
Definitions  List has  heretofore  been or may  hereafter be amended or modified
from time to time in accordance with the provisions of the Liquidity Agreement.

     Section 2. Extension.  Pursuant to Section 3.5 of the Liquidity  Agreement,
the Scheduled  Liquidity  Commitment  Termination  Date is hereby extended until
March 2, 2000.

     Section 3. Document Agent. From and after the date hereof, The Bank of Nova
Scotia is appointed Document Agent.

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                  IN WITNESS WHEREOF, the undersigned have caused this Agreement
to be  executed  and  delivered  by their  respective  officers  thereunto  duly
authorized.

                                 DOLLAR THRIFTY FUNDING CORP.



                                 By:                                            
                                    Name:
                                    Title:



                                 CREDIT SUISSE FIRST BOSTON
                                 NEW YORK BRANCH
                                  as Liquidity Agent



                                 By:____________________________                
                                    Name:
                                    Title:






                                 By:____________________________                
                                    Name:
                                    Title:












LIQUIDITY COMMITMENT                             LIQUIDITY LENDER
- --------------------                             ----------------

$65,000,000                                      THE CHASE MANHATTAN BANK




                                                 By:_______________________     
                                                 Name:   Andris G. Kalnins
                                                 Title:     Vice President