"It has been confirmed that a limited amount of oil has leaked into the sea. We are currently working on mapping the extent of the leak," the company said in a statement Sunday. "The platform has been shut down."
Statoil said an alarm signaling an oil leak was triggered Sunday morning local time. The 270 members of the Statfjord C crew were evacuated to lifeboats but returned to their living quarters later in the day.
No injuries were reported. No announcement was made on when the rig would return to service.
Statoil provided no explanation for the leak but said weather in the area was "harsh."
Emergency responders were observing the situation, the company said.
Statfjord C is one of three rigs operating over the Statfjord field in the North Sea. Statoil said the region is producing an average 80,000 barrels of oil per day.