Suncor Energy has been fined $130,000 for spilling drilling fluid into the ocean 18 months ago, in the offshore field east of St. John's.
More than 26,000 litres of fluid drained from the Henry Goodrich oil rig on March 28th, 2011, after a valve was accidentally left open.
Witnesses said there was a sheen on the ocean surface, which quickly dispersed.
However, a layer of fluid about five millimetres thick and 60 to 80 metres long was later found on the seabed.
Suncor was charged six months ago and pleaded guilty in provincial court on Friday.
The company was fined $30,000, but was also ordered to forward another $100,000 to an environmental damages fund.
Suncor must also post a notice on its website explaining what happened.