Exxon to sell part of Tonen stake for about $3.9 bln: sources TOKYO (Reuters) - Exxon Mobil (XOM.N) plans to sell a large part of its 50 percent stake in TonenGeneral Sekiyu KK (5012.T) back to its Japanese refining partner in a deal that could be worth about 300 billion yen ($3.9 billion), and will make an announcement as early as Monday, sources told Reuters. Exxon Mobil will retain about a 20 percent stake in TonenGeneral but the deal will mark a de facto retreat from the world's third-largest economy by the U.S. oil giant, which is focusing its resources on emerging markets and development of natural resources. ($1 = 76.7350 Japanese yen) Reporting by Taro Fuse and Emoto Emi; Writing by Kaori Kaneko; Editing by Chris Gallagher