Saudi Arabia has approached Exxon to buy a stake in the U.S. company's European oil refining and marketing operations, industry sources said. "The Saudis have been negotiating with at least one of the American partners in Aramco (the Arabian American Oil Co.)," one industry source said. He said the company was Exxon. Neither Exxon, the world's largest oil company, nor the Saudi embassy in Washington would discuss the matter. But industry analysts said they had heard of the talks, which they understood were initiated by the Saudis and were informal.