China National Offshore Oil Corp. announced it restarted operations at the Penglai 19-3 oilfield, the largest offshore field in the country.

CNOOC said it was told in June by the Chinese subsidiary of ConocoPhillips that less than 5 barrels of oil was released at the Penglai 19-3 oilfield in Bohai Bay. CNOOC said the release occurred during an oil transfer but automatic isolation valves closed "immediately," preventing further release.

"Following a series of rectification measures, PL19-3 oilfield has recovered to a normal state," the company said.

In 2011, two leaks at the field released hundreds of barrels of crude oil into the water, resulting in marine pollution and environmental damage to a marine area of 2,400 square miles.