SECOND AMENDMENT TO PARTICIPATION AGREEMENT

Ex hibit 10.18

SECOND AMENDMENT TO PARTICIPATION AGREEMENT

Block 4 Joint Development Zone

This Amendment to Participation Agreement (“Agreement”) made and entered into this 14 th 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 respec