Why pay a penny more for gas than you have to? Unless your car requires high-octane fuel, there's no reason to buy premium, particularly when it can cost as much as 40 cents more per gallon. Ditto for mid-grade: Today's cars are designed to run safely and perform well on regular-octane fuel.
Consumers who own so-called "flex-fuel" cars have the option of using E85, a gas blend that contains 85 percent ethanol, which is usually cheaper -- particularly in the Midwest, where much of the country's ethanol is produced. On the downside, though, a gallon of ethanol contains less energy than a gallon of gas, so unless it's a lot cheaper, the reduced cost may be offset by lower gas mileage. That said, many car owners aren't aware that their vehicles can burn E85, so its worth checking whether yours does.