Norway's Statoil has been fined US$4.26m (NOK25m) for the Statfjord A loading buoy oil leak.
The oil giant was fined by the Rogaland county public prosecutor.
The amount of crude oil leaking into the North Sea on December 12 was about 25,000 barrels, making it one of the biggest oil spill disasters in Norwegian waters.
According to a report by the Norwegian Institute for Nature Research, the Norwegian Institute for Marine Research and the Sintef research foundation, the oil spill did not cause any identifiable harm to the environment.
"We've made changes to the way we plan and implement modifications, strengthened the maintenance programme and adopted more secure routines for offshore loading, said Statoil president for operations Thorstein Hole.