The Erawan gas concession, operated by Chevron Corp, and the Bongkot gas concession, operated by state-backed PTT Exploration and Production PCL, will expire in 2022 and 2023, respectively.

The areas have combined output of 2.2 billion cubic feet a day, about 76 percent of output from the Gulf of Thailand.

The terms for the auction will be announced in July or August this year, Veerasak Pungrassamee, director of the energy ministry's mineral fuels department, told a press conference. "Everything is going according to the ministry's planned timeframe," Veerasak said.

Veerasak did not say when the auctions would be held. Energy Minister Anantaporn Kanjanarat said earlier this year the auctions would be held in December.

An amendment to a petroleum law that will give companies more options on how to manage exploration and production operations will come into effect on Friday.

The amendment, which was approved in March, gives companies the option of striking production sharing agreements (PSA) or service contracts with the government.

Oil and gas companies currently operate fields on a concession basis, paying taxes and royalties on profits.

The energy ministry will next work on laws that set the terms for production sharing agreements and service contracts, Veerasak said.

By Reuter l Reporting by Patpicha Tanakasempipat l Editing by Tom Hogue