The agreement gave the financial framework for the project to begin, ExxonMobil said in a statement.
The agreement was signed in Port Moresby by ExxonMobil vice-president, Bill Threllfall, and chairman of the Gas Committee, Sir Moi Avei, and The Hon Roy Yaki, minister for Petroleum.
The next step was to conclude gas sales arrangements and for the PNG Government to finalise its level of participation.