* Cheniere to supply 3.5 mln tonnes a year to BG * Deal will run for 20 years * BG will ship LNG to markets across the globe By Edward McAllister NEW YORK, Oct 25 (Reuters) - BG Group will export liquefied natural gas from the United States under a landmark $8 billion deal with Cheniere Energy that will allow domestic producers to ship bountiful shale gas supplies to the world for the first time. The deal, announced Wednesday, paves the way for terminal developer Cheniere to secure financing for the its Sabine Pass project in Louisiana which could be the first LNG export plant built in the United States in nearly 50 years as U.S. gas production hits record highs. "If we start construction by next year then we could be exporting by 2015," Cheniere chief executive Charif Souki told Reuters. "The BG Group contract will help with financing." The deal is expected to reap $410 million a year, Souki said, a boon for a company which put most of its money into building a huge import terminal at Sabine Pass that has for three years received only sporadic supply. Record U.S. natural gas production has swamped the market in recent years, leading to a series of rival export proposals all hoping to sell LNG to higher paying markets in Asia and Europe. LNG is natural gas cooled to a liquid for shipping overseas. Under the deal, which could help reverse the fortunes of the troubled Houston-based company, Cheniere will sell 3.5 million tonnes per year of liquefied natural gas to BG for 20 years from its proposed export plant in Sabine Pass, Louisiana. Terminal developers like Cheniere are scrambling to turn their idle import facilities into export plants to ship U.S. natural gas abroad after a revolution in shale gas production left the United States with 100 years of supply. BG Group, one of the world's biggest LNG players, has access to import markets across the globe. Anywhere from Japan to Korea to Chile could soon be importing U.S. gas. Cheniere will sell the LNG to BG for 115 percent of U.S. benchmark Henry Hub prices, plus a $2.25 premium. "The 15 percent will be used for fuel and sourcing the gas, so we will make $2.25 (per million British thermal units)," Souki said. "We haven't decided where we will source the gas from. It will either be from the market or through a supply deal," he said. Sabine Pass will have an initial capacity to export 9 million tonnes per year. Cheniere expects to announce another supply deal soon, Souki said. Five projects across the United States and two in western Canada have applied for construction and export licenses, seeking long term deals predominantly with buyers in Asia where prices are four times higher than those in the United States. FACTBOX: Cheniere is the only project in the United States with a license to ship LNG across the globe. It is now waiting for approval to start construction at Sabine Pass, which will source gas from prolific shale fields in the southern United States for thirsty Asian markets. While U.S. gas prices has fallen under the weight of ample supply, Asian gas prices have rocketed more than 50 percent since March, when an earthquake knocked out a large portion of Japan's nuclear power supply and raised LNG imports. Asian spot LNG prices are now around $17 per million British thermal units, compared to less than $4 in the United States, making export an increasingly viable option.