Sovereign and organizational immunity — Foreign States — International organizations — Whether OPEC a “foreign State” for purposes of service of process under the Foreign Sovereign Immunities Act 1976 — Whether OPEC amenable to service of process under the International Organizations Immunities Act — Whether price fixing activities of OPEC and its member States were “commercial activity” for purposes of amenability to suit under the 1976 Act — Whether OPEC member States were “persons” subject to liability for restrictive trade practices under Section 1 of the Sherman Act — The law of the United States