US energy firm Kosmos Energy has acquired majority rights to one of the oil blocks in Sao Tome and Principe's exclusive economic zone, the company and the African island nation said on Saturday. Kosmos Energy acquired a 65 percent stake in Block 12, meaning that it now has stakes in four of Sao Tome's 19 offshore blocks. Block 12's remaining stakes are controlled by Sao Tome and Principe's National Petroleum Agency and Equator Exploration, according to a statement released by the agency.