UPDATE 1-Santos: Close to securing Gladstone LNG customers

* Two-train Gladstone LNG seen costing less than $15 bln

* Possible to sign sales deal before getting certainty on tax

* Says window of LNG project consolidation may have closed (Recasts, adds details)

BRISBANE, May 19 (Reuters) - Australia's Santos Ltd (STO.AX) is close to securing customers for its Gladstone liquefied natural gas (LNG) project in Queensland state, adding that an expanded two-train gas plant is expected to cost less than $15 billion.

Santos Chief Executive Officer David Knox said the firm was in advanced talks with potential customers for Gladstone LNG and that it was possible it would ink both the gas and equity sales deal before getting clarity on the government's proposed mining tax.

"We are able to do it, but you do it through other commercial agreements. It means the commercial agreements will just get more complicated," Knox told reporters at the sidelines of an energy conference in Brisbane.

Knox also said he was prepared to sell more than the previously stated 9 percent equity stake in Gladstone LNG, should it get the "right customer", although that would require an approval from project partner Petronas [PETR.UL], Malaysia's state-owned energy firm.

China's Sinopec Corp (0386.HK) said on Tuesday it was in contact with Santos for possible LNG supply deals. [ID:nTOE64H04F]

When asked if an expanded two-train facility at Gladstone LNG could cost more than the $15 billion gas export project in Papua New Guinea which Santos has a stake in, Knox said: "I would assume not."

Knox said the $15 billion Papua New Guinea LNG project, led by ExxonMobil Corp (XOM.N), would be more expensive to build due to the technical and geographical challenges.

On the possibility of consolidation of the four planned LNG projects on the eastern Gladstone port, Knox said a merger of plant facilities would bring significant cost savings, but he believed the window of opportunity for such mergers may have closed.

Santos, Australia's largest onshore gas producer, said a final investment decision on Gladstone LNG has now been pushed back to the second-half of 2010, from the earlier mid-year target.

It plans to first make a decision on a single processing train facility with a capacity of 3.6 million tonnes per annum, before approving a second-train expansion a year later. (Reporting by Fayen Wong; Editing by Ed Davies)