The consumer watchdog is probing Woodside Petroleum's $US2.75 billion purchase of LNG assets from a US energy giant, over concerns the deal could lift gas prices.

Woodside announced in December its purchase of Apache Corporation’s stakes in a string of projects, including the Wheatstone LNG venture, which is currently under construction off the coast of Western Australia.

The Australian Competition and Consumer Commission has sent a letter to interested parties, seeking feedback on the possible implications of the deal.

It is seeking feedback on whether Woodside and Apache compete closely and whether the deal will affect wholesale gas prices and production in WA.

Woodside said in December the deal would increase its oil and gas reserves by 20 per cent, and the timing was right to buy into the Wheatstone Project, which is around half complete, despite the recent slide in oil prices.

Under the planned acquisition, Woodside will pay $US2.75 billion ($A2.98 billion) for a 13 per cent stake in Wheatstone, which will be operated by global giant Chevron, as well as a 65 per cent stake in the Balnaves Oil Project, also in WA, and 50 per cent of a Canadian LNG project.