China National Offshore Oil Corporation (CNOOC), the country's largest offshore oil producer, said Monday that the oil leaks have been sealed by reservoir pressure reduction and a series of technological measures in northern China's Bohai Bay.

More than 5,500 square kilometers of water in the Bohai Sea has been polluted by oil spilled at the platform since June, causing the country's worst offshore maritime pollution. [hbsell.com]?

As the majority owner of the leaking Penglai 19-3 oilfield, CNOOC said all oil spill sources have been identified and blocked off at ConocoPhillips' oil platforms in Bohai Bay.

ConocoPhillips China, a subsidiary of the Houston-based energy company ConocoPhillips which has a 49 percent stake in the oilfield in Bohai Bay, said on Monday it is "taking additional measures to monitor the seafloor for activity of previously identified or possible additional seep sources".

"After adopting some effective measures, we believe that we have met the requirements set by the State Oceanic Administration (SOA) to thoroughly examine and block the oil sources and continue to clean up the oily mud," said Chen Bi, executive vice-president of CNOOC, the nation's biggest offshore oil producer.

All oil-based mud in the seabed of platform C has been cleaned or taken under control, said Chen, adding that oil spots detected on the sea surface have been decreasing significantly.

No new leak point had been detected in the seabed of platform C in the past two months, said the company.

However, the information has yet to be confirmed by the national maritime authority, according to China Daily.

A report on the website of the North China Sea Branch of the SOA showed that the daily oil leakage was about 1.67 liters from platform C on Oct 23.

Over 100 divers had been sent underwater by Oct. 14 to clean 22,062 cubic meters of oily water, which included 416 cubic meters of oil-based mud, CNOOC said.

The divers have used covers, like canvases and sandbags, to block off the small amount of oil-based mud that remained unreachable, the company said.

More than 5,500 square kilometers of water in the Bohai Sea has been polluted by oil spilled at the platform since June, causing the country's worst offshore maritime pollution.

The field is being mined by ConocoPhillips China, the U.S. oil giant's subsidiary, under a joint development agreement with CNOOC.