BANGKOK -- Critics on Thursday slammed Thailand's state-owned oil and gas company for its allegedly inefficient response to an oil spill that polluted a popular tourist island, as cleanup operations continued for a sixth day.

About 50,000 liters (13,200 gallons) of crude oil – around the amount contained in 1 1/2 tanker trucks – spilled into the Gulf of Thailand off Samet Island on Saturday morning from a leak in a pipeline operated by PTT Global Chemical Plc., a subsidiary of state-owned PTT Plc.

The spill washed ashore on Samet, a small resort island that each year draws some 1 million tourists due to its pristine beaches and proximity to Bangkok, 140 kilometers (90 miles) to the northwest.

Opposition lawmaker Sathit Pitutecha said Thursday that the operator had failed to plan for such a problem despite previous leaks.

"This is a failure to solve a problem by a company that earns hundreds of billions of baht (billions of dollars) every year, using the country's natural resources," he said during a parliamentary session. "I wouldn't criticize if this was the first time, but it's the fourth time already. Now the people of Rayong (province) have to bear the burden of risk from the industrial sector."

Authorities said Thursday that the oil that blackened the waters off the island had been eliminated, but that some slicks remained onshore.

"We've worked day and night to clean up the bay," PTTGC President Boworn Vongsinudom said from Rayong. "It was supposed to be finished, as we aimed, on the third day, but more oil came in from another spot, so we had to take care of it, too."

Srisuwan Janya, head of the Thailand-based environmental group Stop Global Warming, said the company was neither prepared for the emergency nor frank about the extent of the problem.

"The transfer of crude oil through the pipeline takes place every day, but when an oil spill happens, PTTGC tackled it with unbelievably limited resources," he said. "This shows their solutions are inefficient and not enough."

The company on Sunday had flown in oil spill management experts and a plane from Singapore to get rid of the crude oil, but failed to curb the slicks from spreading.

Environmentalists fear the slow cleanup process will impact the surrounding area.

"It's plain to see that the longer the spill exists, the worse impact it would have on the environment," said Thon Thamrongnawasawat, a marine biologist at Bangkok's Kasetsart University. "But at this point, it is very difficult to estimate the damage the leak has caused to the ecosystem."

PTT is Thailand's largest energy company and one of the biggest listed oil and gas conglomerate in Asia-Pacific.

The incident is the company's fourth major oil spill in Thailand, according to the Energy Ministry.

In 2009, another PTT subsidiary was involved in the Montara oil spill, one of Australia's worst oil disasters, in the Timor Sea off western Australia.

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  • In this photo taken Saturday, July 27, 2013, a cleaning vessel clears the oil after about 50 tons of crude oil was leak from a pipe spilled into the sea off Rayong province, eastern Thailand. The oil spill that leaked from a pipeline, operated by a subsidiary of state-owned oil and gas company PTT Plc, has reached a popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up over the weekend, officials said Monday. (AP Photo/The Nation-Atchara)

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • A shovel sits in oil-covered sand at Ao Phrao beach as volunteers work to clean up the area after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • In this photo taken Saturday, July 27, 2013, cleaning vessels clear the oil after about 50 tons of crude oil was leak from a pipe spilled into the sea off Rayong province, eastern Thailand. The oil spill that leaked from a pipeline, operated by a subsidiary of state-owned oil and gas company PTT Plc, has reached a popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up over the weekend, officials said Monday. (AP Photo/The Nation-Atchara)

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up a major oil slick which coated a beach on a popular tourist island in a national park after a pipeline leak. AFP PHOTO/ Nicolas ASFOURI

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel pour oil off as they clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Streaks of crude oil are seen on the shore of Prao Bay on Samet Island in Rayong province eastern Thailand Monday, July 29, 2013. The oil spill that leaked from a pipeline has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up over the weekend, officials said Monday. (AP Photo/Daily News)

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • People work to clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel work to clean up from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up the major oil slick which coated a beach on the popular tourist island in a national park after a pipeline leak. AFP PHOTO / Nicolas ASFOURI

  • Oil-stained buckets lay on the beach as Royal Thai Navy personel take a break as they clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up a major oil slick which coated a beach on a popular tourist island in a national park after a pipeline leak. AFP PHOTO/ Nicolas ASFOURI

  • Royal Thai Navy personel clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up a major oil slick which coated a beach on a popular tourist island in a national park after a pipeline leak. AFP PHOTO/ Nicolas ASFOURI

  • A major oil slick is seen on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up a major oil slick which coated a beach on a popular tourist island in a national park after a pipeline leak. AFP PHOTO/ Nicolas ASFOURI

  • A resort signage is seen as Royal Thai Navy personel (background) clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up a major oil slick which coated a beach on a popular tourist island in a national park after a pipeline leak. AFP PHOTO/ Nicolas ASFOURI

  • An oil slick on Ao Phrao beach on the island of Ko Samet on July 30, 2013. Thai navy personnel battled to clean up a major oil slick which coated a beach on a popular tourist island in a national park after a pipeline leak. AFP PHOTO/ Nicolas ASFOURI

  • Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • A worker cleans rocks as Royal Thai Navy personnel, Thai Army and local volunteers clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. TOPSHOTS AFP PHOTO / Nicolas ASFOURI

  • People use special paper to soak up the oil as they clean up Ao Phrao beach after a major oil slick hit the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm on July 30 of understating the extent of the major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO / Nicolas ASFOURI

  • Royal Thai Navy personel, Thai army and local volunteers clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm Tuesday of understating the extent of a major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO/ Nicolas ASFOURI

  • Streaks of crude oil cover the shore of Prao Bay on Samet Island in Rayong province eastern Thailand Monday, July 29, 2013. The oil spill that leaked from a pipeline has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up over the weekend, officials said Monday. (AP Photo/Daily News)

  • Royal Thai Navy personel, Thai army and local volunteers clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm Tuesday of understating the extent of a major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO/ Nicolas ASFOURI

  • Royal Thai Navy personel, Thai army and local volunteers clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm Tuesday of understating the extent of a major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO/ Nicolas ASFOURI

  • Royal Thai Navy personel, Thai army and local volunteers clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm Tuesday of understating the extent of a major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO/ Nicolas ASFOURI

  • Royal Thai Navy personel, Thai army and local volunteers clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm Tuesday of understating the extent of a major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO/ Nicolas ASFOURI

  • Royal Thai Navy personel, Thai army and local volunteers clean up a beach from a major oil slick on Ao Phrao beach on the island of Ko Samet on July 31, 2013. Environmentalists accused a Thai energy firm Tuesday of understating the extent of a major pipeline leak as the navy warned the oil slick might reach the mainland. Tourists were leaving the resort island of Ko Samet in the Gulf of Thailand as workers in protective suits used hoses, buckets and shovels to clean up blackened sand and oil which washed ashore on a once-idyllic beach. AFP PHOTO/ Nicolas ASFOURI

  • Workers use buckets to remove crude oil during a clean up operation on the beach of Prao Bay on Samet Island in Rayong province eastern Thailand Tuesday, July 30, 2013. About 50,000 liters (13,200 gallons) of crude oil that leaked from a pipeline operated by PTT Global Chemical Plc, has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up. (AP Photo)

  • Workers use shovels to remove crude oil during a clean up operation on the beach of Prao Bay on Samet Island in Rayong province eastern Thailand Tuesday, July 30, 2013. About 50,000 liters (13,200 gallons) of crude oil that leaked from a pipeline operated by PTT Global Chemical Plc, has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up. (AP Photo)

  • Workers use buckets to remove crude oil during a clean up operation on the beach of Prao Bay on Samet Island in Rayong province eastern Thailand Tuesday, July 30, 2013. About 50,000 liters (13,200 gallons) of crude oil that leaked from a pipeline operated by PTT Global Chemical Plc, has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up. (AP Photo)

  • A worker pours crude oil in to a basket during a clean up operation on the beach of Prao Bay on Samet Island in Rayong province eastern Thailand Tuesday, July 30, 2013. About 50,000 liters (13,200 gallons) of crude oil that leaked from a pipeline operated by PTT Global Chemical Plc, has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up. (AP Photo)

  • Workers remove crude oil during a clean up operation on the beach of Prao Bay on Samet Island in Rayong province eastern Thailand Tuesday, July 30, 2013. About 50,000 liters (13,200 gallons) of crude oil that leaked from a pipeline operated by PTT Global Chemical Plc, has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up. (AP Photo)

  • Workers remove crude oil during a clean up operation on the beach of Prao Bay on Samet Island in Rayong province eastern Thailand Tuesday, July 30, 2013. About 50,000 liters (13,200 gallons) of crude oil that leaked from a pipeline operated by PTT Global Chemical Plc, has reached the popular tourist island in Thailand's eastern sea despite continuous attempts to clean it up. (AP Photo)