Demonstrators called 1 April Fossil Fools Day
Three people climbed onto the roof of a Devon petrol station to demonstrate about climate change.
The protesters, dressed as clowns, were part of a group of about 30 from Rising Tide who occupied the Esso garage on Exeter Street, Plymouth.
Police arrested four people for breach of the peace.
Exxon Mobil, Esso's parent company, said it was taking real and positive action to address the problem of climate change.
A spokesman said: "We deplore the flagrant disregard that the demonstrators are showing for safety and the law. We urge them to make their protests peacefully and legally.
"Exxon Mobil takes the issue of climate change extremely seriously, and is actively working to address the risks it poses."
Rising Tide launched what it called Fossil Fools Day on 1 April to raise awareness of the issue of fossil fuels and the affect of their use on climate change.