Often, the appeal of a smaller car is the potential to save money at the gas pump, but a smaller car doesn't always mean you'll be getting lots of miles per gallon. While smaller vehicles generally boast better fuel efficiency than larger vehicles, individual makes and models can vary greatly. Do your research on a car-by-car basis to determine the gas mileage of each car.

Consumer Reports notes that the transmission on each car may affect the fuel efficiency. Many small cars come with a wider range of gears — four-, five- or, now more commonly, six-speed automatic transmissions — which may result in better fuel economy thanks to the engine running at lower revolutions in higher gears. Smaller rides also tend to rely on continuously variable transmissions (CVTs) instead of traditional gearboxes. (A CVT is an automatic transmission that uses two pulleys connected by a steel belt on cone-shaped pulleys, says Edmunds.) Since a CVT engine is not tied to fixed gears, it keeps the engine at optimum power and may boost fuel economy.

You may also be able to buy a hybrid or electric compact or subcompact car. Consumer Reports suggests determining whether the potentially higher price tag for one of these "green" cars will truly pay off in fuel savings — you may be able to recoup the costs in fuel savings quickly with some models, while it may not pay off with others.