PTT Exploration and Production Plc (PTTEP) may buy additional shares in Mozambique's Rovuma offshore area if other shareholders want to offload their stakes.
The company now owns 8.5% of the project through Cove Energy, which it acquired last year for US$1.9 billion.
Videocon, which owns 10%, wants to sell all its shares, while Anadarko, with 36.5% ownership, reportedly plans to give up a 10% stake.
"We won't rule out buying those shares if the two stakeholders want to offer them to us," said Tevin Vongvanich, the president and chief executive.
With gas reserves of 63 trillion cubic feet, this area is moving into the production phase after several years under exploration.
The first gas production is expected in 2018.
"We won't buy the entire 20% from these two firms, as that would require a very huge amount of money," said Mr Tevin.
He said East Africa has high potential in terms of liquefied natural gas.
The regional gas boom is drawing interest from many energy giants including Shell and Exxon Mobil.
If shares are offered for sale, then PTTEP can mobilise $3 billion to buy them, said Mr Tevin.
The company expects the average total petroleum sales volume this year will increase by 13% to 310,000 barrels of oil equivalent per day from 275,000 BOED last year.
The increase will come from additional production of existing and new projects such as Thailand's South Bongkot and Sirikit 1 fields, 16-1 in Vietnam and Montara in Australia.
The sales volume will increase by almost 10% to 340,000 BOED next year, expected to come from new production projects including Zawtika in Myanmar as well as Algeria.
The company has announced five-year capital expenditures through 2017 of $15 billion.
Of that, 60% will be allocated to exploration and production activities in Thailand, 19% in North America and 18% in Myanmar.
The company projects the average crude oil price will be equivalent to last year's average level of around $110 a barrel.
PTTEP is looking ahead to greater investment in petroleum-rich Myanmar, Australia, North America and East Africa, partly by takeover or merger and acquisition opportunities in the future, said Mr Tevin.
Shares of PTTEP closed yesterday on the Stock Exchange of Thailand at 157.50 baht, down three baht, in heavy trade worth 1.24 billion baht.