All cars come with a Gas Mileage Rating. This is the amount of gas your car will use per mile driven. Two types of gas mileage ratings exist. There is a Gas Mileage Rating for city driving and a Gas Mileage Rating for highway driving. Generally a car will have better highway mileage ratings than city ratings. Also cars with smaller engines will have a better Gas Mileage Rating. Larger vehicles will get less miles per gallon than smaller vehicles. Engine and vehicle size are not the only things that effect gas mileage. The way a person drives will also effect gas mileage.