Exhibit 10.18


SECOND AMENDMENT TO PARTICIPATION AGREEMENT


Block 4 Joint Development Zone





This Amendment to Participation Agreement (“Agreement”) made and entered into this 14th day of March 2006 by and between





ERHC Energy, Inc., a corporation organized and existing under the laws of the State of Colorado, U.S.A. (hereinafter referred to as “ERHC”), and





Addax Petroleum (Nigeria Offshore 2) Limited, a company incorporated in the Federal Republic of Nigeria (hereinafter referred to as “Addax”) and Addax Petroleum
NV, a company incorporated in Curacao, as Parent.





Each of ERHC and Addax is individually a “Party” and they are collectively the “Parties” to this Agreement.








WITNESSETH:





WHEREAS, the Parties have executed a Participation Agreement dated 17 November 2005 (the “PA”) wherein the Parties agreed to the terms and conditions whereby Addax would earn certain rights in Block 4 of the Nigeria-Sao Tome e Principe Joint Development
Zone (the “JDZ”); and





WHEREAS, the Parties have executed an Amendment to Participation Agreement dated 23 February 2006; and





WHEREAS, the Parties now wish to further amend the PA as provided in this Agreement.





NOW, THEREFORE, in consideration of the mutual covenants and agreements herein contained, and other good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, the Parties hereto agree as follows:





1.             We have been advised that the PSC in respect of Block 4 will be executed on 14 March 2006 or later and that the division of interest in the PSC will show that the ERHC/Addax consortium (including preferential rights) will be sixty percent (60%).
In order to give effect to the PA, as amended, Addax and ERHC shall, immediately upon the execution of the PSC execute the letter attached hereto as Exhibit “1” (the “JDA Letter) that will result in Addax owning a thirty-three and three tenths percent (33.3%) interest and ERHC owning a twenty-six and seven-tenths percent (26.7%) participating interest in and to the PSC covering Block 4. ERHC and Addax will do such acts as is necessary to seek approval from the Joint Development Authority to
the JDA Letter and the Assignment.











2.              Except as specifically amended by this Agreement, the PA shall remain unchanged. The Parties hereby affirm and ratify the PA as amended by this Agreement.





Done and executed this 14th day of March 2006.








ERHC Energy, Inc./s/Walter F. BrandhuberWalter F. BrandhuberPresident and Chief Executive OfficerAddax Petroleum (Nigeria Offshore) Limited/s/ I. L. BlairI. L. BlairDirectorFor anion behalf ofAddax Petroleum NVBy:Jean Claude GandurChairman













Exhibit “1”











March 14, 2006





Mr. Carlos Gomes


The Chairman


Nigeria-Sao Tome & Principe


Joint Development Authority


Plot 1101 Aminu Kano Crescent


Wuse II, Abuja


Nigeria








NIGERIA-SAO TOME E PRINCIPE JOINT DEVELOPMENT ZONE - BLOCK 4





Dear Sir:





Congratulations are in order for all involved in the successful execution of the Block 4 PSC on this date.





Please be advised that the interest shown for the ERHC/Addax consortium (including pre-existing rights) as a total of 60% shall be individually owned by Addax in the proportion of 33.3% and by ERHC in the proportion of 26.7%. We have this day entered into an Amendment and Ratification of the JOA executed by all parties
to the PSC and JOA whereby this interest is accepted for ERHC and Addax.





We are looking forward to a long and prosperous project in the development of Block 4.








Sincerely,








ERHC Energy Nigeria Block 3 JDZ Limited
Addax Petroleum (Nigeria Offshore 2) LimitedWalter F. Brandhuber
I. L. BlairPresident and CEO
Director