The offer values the Australian integrated energy player at about $A12.9 billion. When the Australian Securities Exchange closed yesteday, the company's market capitalisation was roughly $A9.2 billion.

Origin said it has not yet considered the proposal.

"Discussions between the parties will take place and shareholders will be advised of the outcome," the company said.

"These discussions may or may not lead to an agreed transaction. Origin shareholders should take no action with respect to their Origin shares, pending further announcement."

This is not BG Group's first move into Australian gas. It is also in the process of becoming a major shareholder in coal seam methane producer Queensland Gas Company. The two companies have joined forces to develop a 3-4 million tonnes per annum liquefied natural gas plant in Gladstone, Queensland.

BG has also been seen by many analysts as a possible candidate to invest in Santos' Gladstone LNG plant, and as a possible predator in takeover move.

However, if BG does acquire Origin, the Australian Competition and Consumer Commission will not allow it take over QGC or Santos. But it could still be in a position to block other predators from acquiring those companies.

But it now seems likely that if the bid for Origin succeeds, BG will simply ignore Santos.

BG Group has advised that the proposal to acquire Origin is subject to shareholder and regulatory approvals and other terms and conditions common to transactions of this type.