A growing number of new vehicles have improved fuel economy but come with manufacturers' recommendations to use premium gasoline, which according to the Department of Energy costs an average of 30 cents more per gallon than regular. Automakers say that as they strive to improve fuel economy, they maintain the performance customers expect by boosting the recommended octane. Some say the relatively stable price spread between regular and premium is due to an increased use of ethanol, which is used by refiners as an octane booster.

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