US oil company ConocoPhillips said on Monday it had cleaned up 99 percent of the mineral oil-based drilling mud near Platform C at Penglai 19-3 oil field, as a deadline ordered by China's oceanic authorities is approaching.

By Aug 29, 399 cubic meters of mineral oil-based drilling mud, accounting for 99 percent of the volume that had been identified on the seabed around Platform C, had been cleaned up, according to a statement on the company's website.

"The mud is expected to be cleaned up completely before the end of August," it said.

The statement is seen as a promise to the Chinese government, as the State Oceanic Administration (SOA) of China had urged the company to finish cleaning up the oil spills in North China's Bohai Bay by Aug 31.

However, the company's statement raised queries among environmental experts and lawyers.

"Currently, it is not clear that all the oil spill sources have been discovered since most of them are 30 to 40 meters under the sea surface and are difficult to see," Wang Yamin, a marine professor at Shandong University, told the portal website Sina on Tuesday.

Among the 16 oil spill spots that were found around Platform C, 12 have disappeared with no new oil leaks observed, ConocoPhillips' statement said.

Of the four other visible oil spill spots in the area, two are still intermittently active and about 1 to 2 liters of oil leaks from them every day, it said.

At Platform B, the amount of the mixture of oil and gas leaked is about 1 liter every day.

The company has covered the spill spots with containment devices on the seabed to capture any oil and prevent it from reaching the surface, it said.

The company estimated that the total amount of oil and other liquid pollutants leaked in this incident reached 1,500 barrels, or 240 cubic meters.

Ma Jun, director of the Institute of Public and Environmental Affairs, a non-government organization based in Beijing, told China Daily on Tuesday that it was obvious the company had tried to shirk its responsibilities since the oil leak accident happened two months ago.

"A third-party institute is needed to supervise the company's moves on cleaning up oil spills as its statements are not reliable any more," he said.

The US company has been widely criticized for its slow response to the oil spills, which have lasted for more than two months and have still not been stopped.

In addition, ConocoPhillips irritated the public with its arrogance. It did not apologize to the Chinese public until Aug 24, more than two months after the oil spill was discovered.

Besides, it has not worked out a compensation plan for the damage the incident has caused to the ocean environment and the fishery industry near the oilfield.