BEIJING China National Offshore Oil Corp (CNOOC), the country's largest offshore oil producer, said all oil spill sources had been sealed at a ConocoPhillips-operated oilfield in the northern Bohai Bay, the Xinhua news agency reported.
The assessment could signal an end to the dispute over the oil spill, which might allow production at China's largest offshore oil field to resume before long.
China's marine authority in early September ordered a subsidiary of Houston-based ConocoPhillips to halt all operations at Penglai 19-3, after it said the company had failed to seal oil leaks that began in June.
The State Oceanic Administration has said the oil spill had polluted 5,500 sq km of Bohai Bay, the most serious marine ecological incident in China.
The spill drew sharp criticism of ConocoPhillips by Chinese media, forcing the oil major to apologize and to establish two funds to clean up and compensate for any damages arising from the incidents.
On Aug 31, ConocoPhillips submitted a report to SOA showing it had sealed off the leaks ahead of the Aug 31 deadline. The company estimated the total amount of oil and mud from oil leaks at around 3,200 barrels.
In CNOOC's latest tests, no new leaks had been detected in the seabed of the platforms B and C in the Penglai 19-3 oil field, Xinhua quoted Chen Bi, vice president of CNOOC, as saying late on Monday.
All oil-based mud in the seabed of platform C has been cleaned and oil spots detected on the sea surface have been decreasing significantly, it said.
The clean-up work has met the requirements of the State Oceanic Administration, it quoted Chen as saying.
ConocoPhillips owns a 49 percent stake in the 168,000 barrel-per-day oilfield and acts as the operator, while China's top offshore oil and gas producer CNOOC Ltd has a 51 percent stake.
(Reporting by Judy Hua and Chen Aizhu)