PERTH - U.S. major Chevron Corp's gas sale agreement with Japan's Tokyo Electric Power is worth A$90 billion ($82.5 billion), and is the biggest Australian LNG supply agreement ever signed, the West Australian government said on Monday.

Japan's top utility TEPCO has signed a deal for 3.1 million tonnes of LNG from Wheatstone a year for 20 year, plus it has bought a 15 percent equity stake in the project that could give it another 1 million tonnes.

TEPCO will also take an 11.25 percent stake in the Wheatstone gas processing facility. The Nikkei newspaper reported on Sunday that TEPCO will invest more than 300 billion yen ($3.34 billion).

Chevron declined to comment on the value.

The first phase of Wheatstone consists of two LNG processing trains with a total capacity of about 8.6 million tonnes per year. Chevron is aiming to approve the project in 2011 and is targetting first LNG shipment in 2016. ($1=1.091 Australian dollar) ($1=89.89 yen) (Reporting by Fayen Wong; Editing by Michael Urquhart)