Exhibit 99.1

                               Joint Filing Agreement

        In accordance with Rule 13d-1(k) promulgated under the U.S. Securities
Exchange Act of 1934, as amended, the undersigned hereby agree to the joint
filing with all other reporting persons on behalf of each of them of all
filings on any Form 3, Form 4, Form 5 or a statement on Schedule 13D or
Schedule 13G, and any and all amendments thereto and any other document
relating thereto (collectively, the "Filings") required to be filed by them
pursuant to the U.S. Securities Exchange Act of 1934, as amended, with respect
to the shares of common stock, par value $0.01 per share, of Montauk
Renewables, Inc., a Delaware corporation, and that this Agreement may be
included as an Exhibit to all such Filings. This Agreement may be executed in
any number of counterparts, all of which taken together shall constitute one
and the same instrument.

        IN WITNESS WHEREOF, the undersigned hereby execute this Agreement as of
February 3, 2022.

                         JOHN A. COPELYN

                         By:   /s/ John A. Copelyn
                               -----------------------------------------------
                               Name: John A. Copelyn


                         CIRCUMFERENCE ENERGY HOLDINGS LP

                         By: Circumference Energy Holdings GP, LLC, its General
                         Partner

                         By:   /s/ John A. Copelyn
                               -----------------------------------------------
                               Name:  John A. Copelyn
                               Title: Sole Manager and Chief Executive Officer