New car engines may be smaller and more fuel efficient, but using less gas does not necessarily mean that you'll be saving money at the pump. The New York Times reports that while the amount of cars requiring premium gas is decreasing, a growing number of automobile manufacturers are recommending premium gas for economy vehicles. The technology used to achieve engine improvements relies on the higher octane levels found in more expensive fuels. Although these cars won't be damaged by regular gasoline, both power and fuel efficiency will suffer, negating most of the benefits of these new engines. So while your new car may get more miles per gallon, you could be making up the cost difference with every refueling.