Chitrapongse Kwangsukstith, PTT's chief operating officer for upstream and gas operations, said the discussions followed a 2006 agreement among the three partners to explore possible investments in LNG.
LNG operations have been delayed for more than a year, after PTT failed to close a supply deal with Iran for LNG from the Pars field in that country due to disagreements on price.
PTT had signed a deal in 2006 with the operators of the Pars field to purchase three million tonnes of LNG per year for 20 years.
PTT president Prasert Bunsumpun said the company needed to move forward with a venture to meet rising gas demand over the next five years.
''We are discussing what share each party should hold. We are not yet at the final stage, but it must be completed soon,'' he said.
PTT would retain a majority share in the proposed LNG import terminal, he added.
PTT, the country's largest energy conglomerate, typically maintained 35% to 45% stakes in joint ventures and generally expresses a preference to hold management authority.
Under the 2006 memorandum of understanding with Egat and Egco, the LNG business would be initiated by PTT, with other partners brought in at different phases to help finance the massive capital investment required by the project.
Mr Chitrapongse said project investment would begin by the end of the year, with the calling of a bid for contractors for the LNG tank terminal and a five-million-tonne storage facility. The terminal is scheduled to start operating in 2011.
The terminal, to be located in the Map Ta Phut industrial area, will be capable of handling the largest LNG supertankers.
On Sunday, PTT executives signed an agreement with Qatargas Operating Co in Doha to purchase one million tonnes of LNG per year with delivery to start in early 2011.
The contract has a 10-year term, and also offers a clause giving PTT priority for another one million tonnes per year of gas if needed.
PTT is also negotiating with other LNG suppliers in Indonesia, with the aim of locking in supplies up to the project's full capacity of five million tonnes per year.
Executives said talks were under way with Australian firms and gas suppliers in the Middle East.
The proposed LNG import terminal could also be expanded to handle double capacity under a second phase if demand growth remains steady.
Piyasvasti Amranand, the energy minister under the Surayud Chulanont government, said the delays in closing the LNG purchase agreement were primarily due to uncertainties about the readiness of Thailand to receive the supplies, and he warned that LNG would cost significantly more than other energy sources used for electricity generation.
Electricity generated from LNG costs around 2.5 baht per unit, compared with two baht per unit for gas sourced from the Gulf of Thailand and Burma or for imported coal.
Hydropower, meanwhile, carries the lowest cost, at 1.8 to 1.9 baht per unit for power transmitted from Laos.
Natural gas already accounts for two-thirds of the fuel used to generate the country's electricity, and authorities say that development of other sources is critical for long-term energy security.
Demand for gas has risen sharply as high oil prices have led firms to switch to gas-driven plants rather than plants using bunker oil and diesel. Consumer use of natural gas for vehicles has also increased thanks to lower prices when compared with diesel or petrol.
PTT shares closed yesterday on the Stock Exchange of Thailand at 326 baht, down two baht, in trade worth 2.56 billion baht.