Six people have been arrested on suspicion of belonging to a gang which was allegedly sending the oil to the Netherlands for processing, police in northwest France said in a statement.
Around 52 thefts were being investigated in the Centre-Val-de-Loire region over the last three months involving the loss of 385 tonnes of oil estimated to be worth more than 460,000 euros ($500,000), the statement said.
Belgian police were also investigating part of the network, which had depots in France and Germany.
Cooking oil from restaurants, once seen as simple waste product, is now a valuable commodity that can be converted into biodiesel.
The oil must be filtered and then is usually combined with methanol to create a fuel that traditional diesel engines can run on.
High crude oil prices have increased demand for such fuels, which has attracted the attention of criminal gangs.
French Police Nab 'Grease Thieves'
FILE: French fries are seen at Mydibel Group factory, a manufacturer of chilled, frozen and dehydrated potato products, in Mouscron, Belgium on April 29, 2020.
RENNES, FRANCE — French police say they have collared a slippery network of cooking oil thieves who had been raiding fast-food restaurants and stealing the discarded contents of their deep fryers to sell as biofuel.