Royal Dutch Shell said on Monday it had brought the oil spill off the coast of Aberdeen under control, but has yet to confirm the extent of the leak.
The slick is estimated at 31 by 4.3 kilometres.
A Department of Energy and Climate Change spokesman was quoted by Channel 4 News as saying the energy firm was still trying to "completely halt" any further leakage.
He also said oil was not anticipated to reach the shore and was expected to be dispersed naturally.
Alex Salmond, leader of the Scottish regional government, told the BBC on Saturday about 100 tons of oil, or about 750 barrels, had leaked into the sea.