A British firm has signed a long-term agreement to buy 3.5 million tons of liquefied natural gas from Cheniere Energy Partners LP's Sabine Pass LNG terminal in Cameron Parish.

BG Group's US-based subsidiary, BG Gulf Coast LNG LLC, signed the 20-year contract, the first long-term liquefied natural gas purchase deal on the Gulf Coast. Cheniere expects to begin building the liquefaction facility in 2012 and to begin exporting LNG as early as 2015.

Martin Houston, BG Group executive director, Americas & Global LNG, said the deal gives BG Group an early entrance into the U.S. gas export market.

"Exports have become and are expected to remain economically attractive due to increases in the North American gas supply base resulting from, among other things, existing and future development of abundant shale gas reserves," Houston said in a news release.