For other types of vehicles, see Alternative fuel vehicle and Hybrid vehicle . The Ford Model T 's engine was capable of running on gasoline or ethanol , or a mixture of the two. A flexible-fuel vehicle (FFV) or dual-fuel vehicle ( colloquially called a flex-fuel vehicle ) is an alternative fuel vehicle with an internal combustion engine designed to run on more than one fuel , usually gasoline blended with either ethanol or methanol fuel , and both fuels are stored in the same common tank. Modern flex-fuel engines are capable of burning any proportion of the resulting blend in the combustion chamber as fuel injection and spark timing are adjusted automatically according to the actual blend detected by a fuel composition sensor. Flex-fuel vehicles are distinguished from bi-fuel vehicles , where two...