Gabon was admitted to UN membership on 20 September 1960, and it has become a member of ECA and all the non-regional specialized agencies. Gabon is also a member of the African Development Bank, G-77, the AU, the ACP, and the WTO, and a signatory to the Law of the Sea. The OAU summit conference was held in Libreville in 1977. Together with the Central African Republic, the Congo, Chad, and Cameroon, it forms the UDEAC, a customs union in which merchandise, property, and capital circulate freely. Libreville is the headquarters for the 12-member African Timber Organization of timber exporters and for the Economic Community of Central African States, consisting of the UDEAC countries and five others. Gabon left OPEC in June 1996.