Staffers on the Senate's Permanent Subcommittee on Investigations pointed to arrangements between the oil companies and entities controlled by the family of President Teodoro Obiang Nguema, as well as to scholarships doled out to relatives of the country's elite...The oil executives contended their transactions were legal and as transparent as possible. [refers to ExxonMobil, Marathon, Amerada Hess - also refers to Riggs Bank]...Two Houston-based oil-field service firms, Halliburton Co. and, most recently, ABB Vetco Gray [part of ABB], have admitted to making improper payments in Nigeria.