A flexible-fuel vehicle (FFV) or ual-fuel vehicle (also sometimes called only flex-fuel) is an automobile with a multifuel engine that can typically use different sources of fuel which are either mixed in the same tank or with separate tanks and fuel systems for each fuel. A common example is a vehicle that can accept gasoline mixed with varying levels of bioethanol (gasohol). Some cars (see bi-fuel vehicle) carry a natural gas tank making it possible switch back and forth from gasoline to natural gas.