Chip fat and other oils are considered waste, so when they are used to make biodiesel it saves carbon emissions by displacing fossil oil. But such is the demand across Europe that imports now account for more than half of the UCO that's made into fuel. According to the study, there's no way to prove these imports are sustainable. With no testing of what's coming in, experts believe it is also ripe for fraud. While UCO is considered a waste material in the UK, in China, Indonesia and Malaysia it has long been used to feed animals. The report raises the question of what people in these countries are replacing the UCO with, when it is exported.