The July 27 leak occurred in PTT Global Chemical Plc's pipeline at a mooring used to transfer oil from the seabed to a tanker off the eastern province of Rayong, threatening a major tourist site, Ao Prao beach on the island of Koh Samet. Roughly 13,200 gallons of oil leaked into the sea.
PTT Global Chemical is a part of the state-owned oil and gas company, PTT Plc, known as PTTEP, Thailand's largest energy conglomerate.
Seeking to contain the damage as quickly as possible, PTT Global Chemical sought assistance from the regional office of Oil Spill Response Ltd. in Singapore to send experts.
PTTEP released a statement apologizing for the spill.
"As of today, the oil leak's impact at Prao Bay has been solved and the emergency situation there has now been terminated," the statement said. "The next phase is the recovery of the environment of which a plan is being prepared. This includes a plan for assisting the affected victims of the situation."
Thailand's Energy Ministry said the incident is the fourth major oil spill in Thailand's history. In 2009, another PTTEP subsidiary was involved in the Montara oil spill, one of Australia's worst oil disasters, in the Timor Sea off Western Australia.
In the aftermath of the incident, Energy Minister Pongsak Raktapongpaisal ordered the overhaul of measures currently applied by petroleum producers in maritime, pipeline and road transport.
"I can assure the public that we have responded to this incident 100 percent with the procedures and equipment that we have on hand," the Bangkok Post Wednesday quoted him as saying.
Siri Jirapongphan, executive director of the Petroleum Institute of Thailand, said though Thailand "has adopted strict standards and applied best practices, with regular drills aimed at preventing and tackling accidents ... we can build on those standards by identifying and addressing weaknesses.
"The open sea off Rayong is subject to strong winds, and thus equipment deployed for an accident such as occurred there should be appropriate."
After meeting with 50 petroleum transport operators, Pongsak ordered the reform of maritime pipeline and road transport rules.
The spill has the potential to affect Thailand's tourism industry, which is an important source of national revenue. In 2012 Bangkok became the world's most visited city, with 15.98 million international visitors spending at least one night.
But reining in PTTEP is a difficult issue, as the company is quite diversified and has invested in 41 exploration and production activities with investments in Thailand, Malaysia, Indonesia, Cambodia, Myanmar, Vietnam, Oman, Egypt, Algeria, Bahrain, Australia, New Zealand and Canada.