LONDON (AP) - Royal Dutch Shell said Tuesday that a leak at one of its North Sea oil rigs has been reduced to 2 barrels - or 84 gallons - a day.
Glen Cayley, technical director of Shell's European exploration and production activities, said the company "deeply regrets" the spill, Britain's worst in a decade.
In an interview with the BBC, Cayley said an investigation is under way to determine the cause of the spill, which was first noticed Wednesday.
"We've got a very complex sub-sea infrastructure and the position of the leak is in an awkward place with a lot of marine growth," he said.
"It's taken our diving crews some time to establish exactly and precisely where that leak is coming from."
Cayley said Shell informed British government agencies of the spill straightaway, but did not make it public until Friday.
The company estimated Monday that 54,600 gallons of oil had spilled into the North Sea from the rig off Scotland's eastern coast, and the leak was continuing at 5 barrels a day.
Cayley said that at its largest point the oil sheen, or oil on the surface of the water, covered an area 19 miles wide by 2.7 miles long (31 kilometers by 4.3 kilometers).
He said most of it has now been dispersed by strong waves.
The Gannet Alpha oil rig, 112 miles (180 kilometers) east of the city of Aberdeen, is operated by Shell and co-owned by Shell and Esso, a subsidiary of the U.S. oil firm Exxon Mobil.
The British government said the leak was small compared with the BP spill in the Gulf of Mexico last year - which dumped 206 million gallons of oil into the Gulf - but said it was still substantial for the U.K.'s continental shelf.
It backed up Shell's predictions that the oil would disperse naturally.