BEIJING - It is possible that small oil spills are continuing at the Penglai 19-3 oilfield, according to satellite images from Sunday that appear to show a fresh belt of oil in the area that was hard hit by leaks in recent weeks.

A joint supervision team from the State Oceanic Administration (SOA) and China Marine Surveillance is on site and has asked ConocoPhillips China, the operator of the oilfield, to explain why oil still appears to be leaking.

The company has been asked to find out what is going on as soon as possible and release the information to the public, according to a notice on the SOA's website on Monday.

The team criticized ConocoPhillips for its slow action in finding out what had caused the leak and asked the company to examine all areas that might have been affected by the oil leak and block all spill sources.

ConocoPhillips China declined to offer any comment on Monday.

The Penglai 19-3 oilfield is China's largest offshore oilfield. ConocoPhillips holds a 49-percent stake in the project while China National Offshore Oil Corporation (CNOOC) holds the rest.

Spills in the oilfield were first detected on June 4 but neither ConocoPhillips nor CNOOC offered a detailed explanation of what happened.

On July 5, the SOA held the first formal news conference about the spills. The SOA said the first leak, which was detected from Platform B, occurred on the seabed and resulted from increased pressure when water was injected into the well. A second incident at Platform C was said to have been due to a surge in the well.

As of July 4, the oil spills had polluted an area of more than 840 square kilometers in Bohai Bay, degrading the water quality from Level 1 to Level 4, which means it became about as clean as wastewater from a sewage out-flow, according to the SOA's statistics.

Dead seaweed and fish were found in the area.

Recent oil samples taken from Changdao, Daheishan and Daqin islands in Shandong province were not the same type of oil as the one that spilled in the recent incidents, said a notice released on the SOA's website on Saturday.

The reason for the death of the fish remains unclear because the amount of petroleum found in their bodies was within safety standards, according to the notice.

Zhai Yuxiu, deputy director of the National Center for Quality Supervision and Testing of Aquatic Products, told China Daily the reason for the fish deaths was complicated. Even a small change in temperature or oxygen density can kill seaweed and fish. Zhai said there was no doubt that a sudden change in water quality would kill seaweed and fish.

Wang Yamin, a professor from the College of Marine Studies at Shandong University in Weihai, said 840 square kilometers of seawater that was polluted to Level 4 indicates that more water surrounding that body of water might have been degraded to Level 2 or Level 3.

"The oil sample testing tells us that the marine environment in Bohai Bay is not good if there have been so many leaks of oil from unknown sources and we must question the safety of aquatic products," Ma Jun, the director of the Institute of Public and Environmental Affairs, said on Monday.

Eleven environmental protection organizations plan to file a joint lawsuit against ConocoPhillips China and CNOOC this week connected to the leak.

"The lawsuit will focus on three aspects: the cleanup of the oil leak, the recovery of the polluted sea area and compensation for the victims," said lawyer Wang Haijun from Beijing Deheheng Law Firm.

He said the environmental groups with the help of his law firm will call for a compensation fund to be established for economic victims of the oil leaks, along the lines of what BP did last year following the Gulf of Mexico oil spill.