BP Amoco agreed to buy Exxon Mobil Corp.'s 30% stake in their European gasoline station joint venture for about $1.5 billion. The European Union said in September that Mobil Corp. would have to sell the stake to win approval of its purchase by Exxon Corp. Exxon completed its $80-billion takeover of Mobil last week, forming the world's largest publicly traded oil company. London-based BP Amoco, the world's third-biggest publicly traded oil company, said the companies also will split their European lubricants alliance as a result of regulators' concerns. Irving, Texas-based Exxon Mobil will receive 51%, including 10 factories and the industrial lubricants business, while BP Amoco gets the motor oil unit, including the Duckhams brand. The companies expect to complete the transaction on Jan. 1. On the New York Stock Exchange, BP Amoco's American depositary receipts closed off 75 cents at $59.25, while Exxon Mobil closed unchanged at $83.88.