The European Union’s imports of used cooking oil — a biofuel ingredient — are raising fears over fraudulent supplies and undermining the bloc’s sustainability push, according to an advocacy group.

The region is overwhelmingly reliant on imports of used cooking oil and consumption more than doubled between 2015 and 2022, with the bulk being used in cars and trucks as biodiesel, Transport & Environment said in a report. Some 60% of the shipments come from China, it said.

But concerns have mounted that some suppliers in Asia are mixing fuels with cheaper feedstocks or less sustainable alternatives and mislabeling them to benefit from renewables incentives. That could include palm oil, a major driver of deforestation in countries like Indonesia. That’s one of the commodities the EU is banning imports of if the supplies were grown on deforested land.

There isn’t a standardized EU method to test used cooking oil, and certification to ensure biofuel meets the bloc’s criteria is done by private programs, making it hard to check, T&E said. With import needs set to grow amid rising demand for ingredients used in sustainable aviation fuel, more needs to be done to increase transparency and public disclosure of information about biofuels, the Brussels-based group said.

“Europe is being flooded with dodgy used cooking oil,” Barbara Smailagic, biofuels expert at T&E, said in a statement. “We need greater transparency and a limit on imports to avoid UCO simply becoming a back door for deforestation-driving palm oil.”