Winter-grade gasoline is a type of gasoline that is used during the winter months when temperatures are colder. It has a higher Reid Vapor Pressure (RVP) than summer-grade gasoline, which means it evaporates more easily and allows cars to start in colder weather. Winter-grade gasoline usually contains more butane, which is less expensive than other gasoline components and has a high RVP, making it easier to mix air and gasoline together, which helps the engine start in colder temperatures. However, this added butane makes the gas slightly less energy-efficient. Winter-grade gasoline is cheaper to produce than summer-grade gasoline, which is part of the reason why gas prices tend to drop during the winter months. The switch from summer-grade gasoline to winter-grade gasoline happens over the course of several months in the fall as temperatures drop and to facilitate lowering the RVP of remaining inventories of summer-grade gasoline.