Energy giant Chevron Australia has signed deals worth up to $70 billion to supply liquefied natural gas (LNG) to Japan and South Korea over the next 25 years.

Chevron says it will supply Osaka Gas and Tokyo Gas with a total of nearly 2.5 million tonnes of liquefied natural gas a year.

In a separate deal, Chevron will provide the South Korean energy company GS Caltex with 500,000 tonnes per year.

The gas will come from the Gorgon gas fields off the Western Australian coast.

Prime Minister Kevin Rudd has told Parliament the project will provide an enormous boost to the national economy.

"These are massive projects that will generate economic growth, income, jobs and prosperity for the nation for decades to come," he said.

"In light of this announcement, I would congratulate Chevron Australia; these sales do not come to pass easily.

"I'll also congratulate our counterparts in the Western Australian Government."

Last month ExxonMobil signed a $50 billion deal with China to supply 2.25 million tonnes of gas over the next two decades, also from the Gorgon gas field.

The Gorgon project, a joint venture between Chevron, ExxonMobil and Shell, is expected to generate $40 billion in Government revenue and create 6,000 jobs at the peak of construction.

The West Australian Opposition Leader Eric Ripper has welcomed the agreement but says the State Government has to make sure the investment translates into work for West Australians.

"There needs to be a strong focus on local content to make sure that the state and its people get full benefit from these massive investments in prospect," he said.