The boss of one of Australia's biggest oil and gas firms says the big fall in oil and liquefied natural gas prices over the past year could see Australia's future export earnings from the LNG boom cut by 50 per cent.

Australia is set to rival the gulf state of Qatar as one of the world's largest LNG producers in a few years time, with earnings of as much as $70 billion in 2018 from LNG exports once predicted.

But the managing director of the Australian listed Oil Search, which owns nearly one third of one of Papua New Guinea's major resources projects, PNG LNG, said Australian Government revenue from the LNG boom could be far less than expected.

"It will be a very good revenue but a lot less than originally thought," Peter Botten said in an interview with the ABC's PM program on the sidelines of last week's Citi Australian and New Zealand Investment Conference in Sydney.

"Australia is a world scale LNG producer and when these major projects are completed, Gorgon, Wheatstone, Ichthys, Australia will have a huge revenue stream from LNG and a very important revenue stream and a very important industry for the country.

"However, if the oil price is halved and the gas prices have halved that revenue stream will be a lot less than was anticipated even 18 months ago."

He estimated the revenue for Australia from LNG exports could be half previous estimates.

"Gas pricing has gone from $US15 in MBTU (one million British thermal units0 down to $US7, so 50 per cent less I would suggest," Mr Botten said.

By Sue Lannin