Attackers vandalized an oil installation run by a French oil company in Nigeria's restive southern region. No injuries, kidnappings or production cuts were reported.
Total SA spokeswoman Patricia Marie said an unknown number of intruders climbed onto an oil rig outside the oil city of Port Harcourt Sunday night.
The attackers caused "a couple of barrel's worth" of oil to spill, but production wasn't affected, she said.
Local residents spotted the intruders and alerted Total, she said. It was not clear whether any arrests were made, Marie said.
"Everything quickly returned to normal and there were no injuries," she added.
Attacks by militants demanding a greater share of oil revenues for their region and communities protesting pollution and underdevelopment have cut crude production in the Nigeria by around a quarter in recent months.
The restive southern Niger Delta region remains deeply impoverished despite producing tens of billions of dollars in oil revenues annually as the heart of Africa's largest oil exporter.
Also on Monday, Royal Dutch Shell PLC announced the reinstatement of 170,000 barrels of daily production lost during community protests that earlier closed an installation.
Since December 2005, several major pipelines have been bombed and about 180 expatriate workers have been kidnapped.
Attacks on oil installations have become an almost daily occurrence following flawed elections last month, which saw the notoriously corrupt ruling party returned to power with a landslide victory in elections the opposition says was rigged. International observers said the vote was not credible.
There have also been several attacks on police and government officials.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969