"The Renewable Transport Fuel Obligation (RTFO) order obligates fossil fuel suppliers to produce evidence showing that a percentage of fuels for road transport supplied in the UK come from renewable sources and are sustainable, or that a substitute amount of money is paid. All fuel suppliers who supply at least 450,000 litres of fuel a year are obligated. This includes suppliers of biofuels as well as suppliers of fossil fuel." (Quoted from article)