ORIGIN Energy and ConocoPhillips have agreed to sell $70 billion worth coal-seam gas to Sinopec through a non-binding deal that would see the state-owned Chinese oil company boost its stake in Gladstone's biggest proposed liquefied natural gas plant to 25 per cent.

The gas deal, if it becomes binding, will support a $US6bn ($5.9bn) second LNG production train for the Australia Pacific LNG joint venture, which has started construction on a $US14bn first train.

The deal comes in spite of concerns over the European sovereign debt crisis and its impact on global economic growth, particularly fears over fallout in China, which counts Europe as its largest export destination. But massive energy deals continue to be signed as China and its corporate proxies look through what is expected to be the next few years of a mixed economic picture.

Origin yesterday announced a "non-binding heads of agreement" to sell Sinopec an extra 3.3 million tonnes of LNG a year between 2016 and 2035, meaning APLNG was on track to formally approve a second train at Gladstone early next year.

 If it goes ahead, the deal will mean Sinopec, which already has a 15 per cent stake in the project and has committed to 4.1 million tonnes of annual supply, has agreed to take about $160bn of LNG over the next 20 years and, with an extra $US1bn payment, will move to a 25 per cent stake in APLNG.

Origin would only say the terms were "consistent" with Sinopec's April deal to enter the project, in which Sinopec paid the joint venture $US1.5bn to take a 15 per cent stake, with market estimates of the sales deal worth $90bn.

"Should this non-binding agreement convert into a binding one, that means the first and second trains for APLNG are fully sold," Origin chief executive Grant King said yesterday.

But in a signal CSG ambitions of the four planned Gladstone gas exporters could be being tempered, Mr King has ruled out pushing ahead with a third-train expansion until the ability to deliver existing plans is proven.

He said the first stage of APLNG, which was approved in July, remained on track for mid-2015 first exports, despite increased opposition to CSG production in Queensland.

"We don't believe the current issues in Queensland will cause our project to be delayed," Mr King said.

Mr King said Origin was unlikely to start marketing for a third train before 2013, and even then this would be early. He said the focus would be on getting the two trains in production first and that APLNG would not be trying to expand the plant.

This is a marked difference from APLNG's Gladstone CSG competitor BG Group, whose chief executive Frank Chapman has said he wants to approve a third LNG train by mid-2012 to take advantage of the economies of building extra trains one after the other.

Origin and ConocoPhillips have better gas resources than BG Group (and the other CSG proponents, Santos-Petronas-Total and Shell-PetroChina), so would be well placed to move quickly on extra trains if they believed the demand was there and had confidence in both their ability to deliver and the economics of producing that much LNG.

A BG spokesman yesterday said the Gladstone plant, named Queensland Curtis LNG, was targeting a final investment decision on a third train next year, but would not say that mid-2012 was still the target.

The Sinopec deal will mean the APLNG stakes of Origin and Conoco both slip to 37.5 per cent.

Deutsche Bank said the deal bolstered the chance of a second train being approved, but that APLNG's first-quarter target was looking "tight" because approvals from the Australian Foreign Investment Review Board and Beijing were required before this.