Azerbaijan has 57 oil fields, 18 of which are offshore, in the Azerbaijani sector of the Caspian Sea. The essential part of the company's revenue comes from the giant ACG oil field complex and Shah Deniz gas field. In September 1994, SOCAR entered into a Production sharing agreement (PSA) with the foreign oil companies led by BP for the 30-year development of the ACG oil field which was later known as the "Contract of the Century". Two years later Shah Deniz PSA was signed. As of 2014 SOCAR holds 11.6% of the ACG shares and 16.7% of the Shah Deniz shares. Moreover, SOCAR operates a number of onshore fields on its own which is the main source of the domestic supply.