Biodiesel is a generic name for a variety of similar fuels that can be used in place of fossil diesel. In general, you would need to either alter vegetable oil to make it chemically similar to diesel, or alter your engine so that straight vegetable oil (SVO) can be used as fuel. Waste cooking oil can be used if it is carefully filtered to prevent damage to the engine from dissolved fats and food particles.
However, if you are thinking of undertaking the conversion of oil or of your car then bear in mind that only very limited quantities of used cooking oil are available, and the production of biodiesel from new vegetable oils can have a very high environmental impact. There may also be little cost saving overall.
Carbon emissions from biofuels can be very high, due to land use changes such as deforestation and from the fuel and fertiliser needed to grow and process the crops. When all factors are included, it is unclear if biofuels have lower greenhouse gas emissions than the fuels they replace. There are also concerns about impacts on biodiversity and water availability, and competition for land needed to grow food.
In our Zero Carbon Britain report we advocate the use of electric vehicles alongside a reduction in private car use as the way to reduce carbon emissions from road transport.
Making 'second generation' biofuels from wood or grasses causes fewer problems, but there will still be limits on the land available. If some biofuel can be produced sustainably, it’s best used where electricity cannot be – such as shipping, some heavy goods vehicles and farm machinery, and aviation.