The leak was discovered on Saturday in a pipe connecting one of PTT's main pipelines in the Gulf with its Platong field, the firm said in a statement.

The Platong field is located about 250 km (155 miles) off the coast of southern Surat Thani province.

"The company is fixing the problem and investigating the cause of incident," it said, adding PTT would use a remote-operated underwater vehicle as part of an assessment process to determine how long it would take to repair the leak.

To offset the gas losses, PTT would allocate 30 million litres of fuel oil, liquefied natural gas and other gas from additional sources, it said. The move would be sufficient to meet existing demand, it said.

The gas leak would impact gas delivery to the Electricity Generating Authority of Thailand (EGAT) and its gas separation plant, PTT said.

EGAT Governor Suthat Pattamasiriwat said the leak was expected to affect total power generating capacity of about 3,000 megawatts (MWs), equal to four to five power plants.

Thailand uses as much as 70 percent of natural gas for electricity generation.

"People might have to pay higher electricity prices from using different types of fuel, depending on how fast PTT can fix the problem and when it can resume gas transmission as normal," Suthat said.

Norkun Sittiphong, permanent secretary at the Ministry of Energy, said the ministry would hold a committee meeting on Monday to discuss its fuel management plans following PTT's natural gas leak.

PTT said the incident would not have an impact on ecology underwater or pose a threat to seawater as natural gas is lighter than air and does not dissolve in water.

Copyright Reuters, 2011