Greenpeace activists claim to have forced more than 100 Esso petrol stations across Britain to close in a protest against the company's support for war.
Up to a thousand staff at the firm's Surrey headquarters have also been sent home after a blockade there raised safety fears.
About 300 Greenpeace protesters are taking part in the day of action against Esso and its parent company, Exxon Mobil, Corporation in protest at the company's alleged support for war and environmental crimes.
A Greenpeace spokesman said: "The action comes in response to Esso's ongoing campaign to keep the US hooked on oil, fuelling war and causing global warming".
The spokesman said that action in 17 counties, including in Wales, East Anglia, Yorkshire and the Midlands, would carry on "until everyone was arrested". At least seven of its activists were being held by police, according to the environmental group.
Greenpeace said the activists had found a way of turning off the oil supply at the petrol stations.
But an Esso spokesman says he knows of only one petrol station that has been affected. "People have every right to express their views but it is ludicrous to suggest that ExxonMobil is in any way encouraging a potential war in Iraq," he said.
PA