According to documents obtained by The Times, nearly two-thirds of Somalia was allocated to the American oil giants Conoco, Amoco, Chevron and Philips in the final years before Somalia's pro-U.S. President Mohamed Siad Barre was overthrown and the nation plunged into chaos in January, 1991. Industry sources said the companies holding the rights to the most promising concessions are hoping that the Bush Administration's decision to send U.S. troops to safeguard aid shipments to Somalia will also help protect their multimillion-dollar investments there.