The flow of oil from the worst spill in UK waters in the past decade, at one of Shell's North Sea platforms, has been "greatly reduced" but not yet stopped completely, the government said on Monday.
Conservationists warned that the leak could harm bird life in the area, at a delicate time in their development, as the oil company worked to minimise the damage.
Stuart Housden, director of RSPB Scotland, said: "We know oil of any amount, if in the wrong place, at the wrong time, can have a devastating impact on marine life. Currently thousands of young auks – razorbills, puffins and guillemots – are flightless and dispersing widely in the North Sea during late summer. So they could be at serious risk if contaminated by this spill."