Thailand's PTT said on Wednesday all of its six gas separation plants were operating normally despite a loss of supply after a leak in an offshore gas pipeline.

One plant that had been shut for maintenance this month had resumed operations and did not require a large amount of gas during the initial period, Wichai Pornkeratiwat, senior executive vice-president for its gas business, told reporters.

"Our gas plants are running as normal because we try to manage our gas supply," Wichai said.

Wichai said PTT continued to supply gas to the petrochemical plants run by its PTT Chemical (PTTCH) at the minimum level required in their contract, which should not affect production at the country's top olefins maker.

PTTCH, which is in the process of merging with PTT Aromatics and Refining, will still shut down its 1 million ton ethane cracker for maintenance on July 15, he said.

"We were informed that PTTCH won't change its shutdown plan to be earlier than scheduled as many had expected," he said.

The natural gas leak in the Gulf of Thailand could result in a loss of about 600 million f³/day (mmcfd),  accounting for around 14% of PTT's total gas supplies in the country, which uses natural gas to generate 70% of electricity.

State-controlled PTT plans to import about 30 million liters of low-sulfur fuel oil from Singapore to offset the shortfall.

PTT, the country's sole gas supplier, is also seeking a fourth shipment of about 70,000 tons of liquefied natural gas (LNG) in the spot market from Qatar to ease tight supplies.

Chief Operating Officer Pailin Chuchottaworn said the leak may have been caused by a ship owned by contractor Hyundai Heavy Industries dumping an anchor in the sea and accidentally hitting the pipe.

"We have to investigate whether the damage was caused by the anchor and assess the damage. If it was, the contractor has to be responsible for this," said Pailin, who will take over as PTT's chief executive in September.

PTT is waiting for equipment from Singapore before sending divers to close a valve on the pipe on July 2, Pailin said, adding that it could then fully investigate the damage and repair the pipe within a few weeks.

Analysts said the gas leak was not a major problem, although by some estimates it could cut PTT's 2011 earnings by as much as 2% if it took a month to fix the problem.