There are several ways to compare gas mileage between vehicles including checking the window sticker at a car dealership or looking up the gas mileage on a car manufacturer website and comparing the results manually. It is also possible to use the comparison tool provided on the U.S. Department of Energy website, which compares the gas mileage of up to four vehicles at once.
To compare the gas mileage of vehicles manually, you can find the information either on the window sticker of the car at a dealership or on the car manufacturer's website. At a dealership, look for the EPA section of the sticker which displays three main gas mileage numbers - city, highway and combined. Alternatively, check the model of the vehicle on the car manufacturer's website where the mileage is displayed in the vehicle information section. You can then compare as many vehicles as you wish by writing down the numbers and checking which vehicle has the best gas mileage.
Another way to check is by using the U.S. Department of Energy website which provides a free tool for comparing the gas mileage of up to four vehicles at once. Simply select the year, make and model of the vehicles you wish to compare, and the tool then displays the appropriate gas mileage side-by-side.