LAGOS (AFP) -- British firm BG Group has signed a sale and purchase agreement to buy 2.5 million metric tones of liquefied natural gas from Nigeria, an official statement said Tuesday.

Under the deal, BG Group will acquire the gas for 20 years from the seventh production line of Nigeria Liquefied Natural Gas (NLNG) in Finima, Bonny Island, Rivers State.

It said cargoes will be delivered to BG's north American marketing business at Lake Charles, Louisiana, in the United States.

"This agreement with NLNG adds to our existing supply arrangements through trans 4 and 5, which came into effect last year," BG executive vice president Martin Houston said.

"It enhances the profitable long-term growth of BG's LNG supply portfolio and reflects the strength of BG's competitive position in the Atlantic Basin," he added. A spokesman for the Nigerian gas firm confirmed the deal, saying "we are excited about the agreement. It is a continuation of our long standing business relationship with BG."

The multi-billion-dollar NLNG, which is co-owned by the state-run oil operator NNPC, Anglo-Dutch group Royal Dutch/Shell, Italy's Agip and France's Totalfina Elf, started operations in October 1999.

The massive LNG taps Nigeria's massive gas reserves and aims to reduce the wastage of gas associated with the country's major oil industry. It has buyers in Europe and the US.