UPDATE: India's Petronet LNG in Initial Pact to Buy US LNG

-- Petronet LNG signs pact to import 4 million tons LNG a year

-- Final agreement on imports is expected by end of 2013

-- Supply of LNG likely to start in 2017-18

(Adds analyst note, other background on LNG imports)

By Debiprasad Nayak and Eric Yep

MUMBAI--India's state-run Petronet LNG Ltd. (532522.BY) said Thursday that it has signed a preliminary agreement with U.S.-based United LNG LP to purchase around 4 million metric tons a year of liquefied natural gas for 20 years.

India's natural gas importers are fast sealing deals to secure supplies as demand far exceeds domestic output. The nation currently produces about three-quarters of its natural-gas requirements, but will need to import nearly half of its requirements within a few years due to dwindling production. Several gas-fired power plants are already shuttered or operating below capacity due to a shortage of gas.

In a statement, Petronet LNG said it expects to finalize the agreement by the end of this year. The supply of LNG could begin sometime in 2017-18, R.K. Garg, Petronet LNG's director of finance, told television channel CNBC TV18.

Buyers in Asia are looking to the U.S. to meet their increasing energy requirements, as the shale revolution has left North America with a huge surplus of gas and prices that are far below those in Asia or Europe. LNG prices in Asia are often several times higher than in the U.S. because of a regional supply deficit. Japan, the world's biggest importer of LNG, pays about $18 per million British thermal units, versus $4 in the U.S.

While the U.S. has a surplus of cheap gas now, rising import demand from Asian countries is likely to raise hackles among some U.S. industry groups and lawmakers who have recently been advocating strict limits on energy exports to Asia citing potential increases in domestic fuel prices.

Petronet LNG said United LNG would supply the super-cooled gas through the Main Pass Energy Hub based off the Louisiana coast in the southern U.S.

In 2011, GAIL (India) Ltd. (532155.BY), a state-run gas processing and distribution company, signed a contract to buy around 3.5 million tons of LNG annually for 20 years from Cheniere Energy's (LNG) Sabine Pass facility in Louisiana.

A boost in LNG exports would have many positive effects on both the U.S. and Indian economies, Nirupama Rao, India's ambassador to the U.S., wrote in The Wall Street Journal earlier this month. "For the U.S. it would help create thousands of jobs and an expanded revenue stream for the federal government. For India, it would provide a steady, reliable supply of clean energy that will help reduce our crude oil imports from the Middle East and provide reliable energy to a greater share of our population," she wrote.

Write to Debiprasad Nayak at [e-mail] and Eric Yep at [e-mail]

Subscribe to WSJ: http://online.wsj.com?mod=djnwires