Last year, Americans spent more that $2 billion pumping premium-grade gas into cars that don't need it, according to a new study from AAA.
Premium-grade gas is specifically formulated to be compatible with specific types of engines and contains a higher octane rating.
Drivers see the 'premium' name at the pump and may assume the fuel is better for their vehicle.
John Nielsen, AAA's managing director of Automotive Engineering and Repair, cautioned drivers that premium gasoline only means higher octane, not higher quality.
He said drivers should follow the owner's manual recommendations for their vehicle's fuel.
The study found that 70 percent of U.S. drivers own a vehicle that requires regular gasoline, as opposed to the 16 percent who drive vehicles that require premium fuel.
Despite that, the study found that in the last year 16.5 million drivers unnecessarily filled their tanks with premium gas an estimated 270 million times.
In the Washington metro area, the average cost of gallon of premium gas is $2.79, according to AAA. That's almost 60 cents more that the average cost of regular unleaded gas.
In tests AAA conducted in partnership with the Automobile Club of Southern California's Automotive Research Center, AAA ran regular and premium fuels in engines that were designed to run on regular.
The study found that premium-grade did not produce more horsepower, better fuel economy or lower tailpipe emissions.
A previous AAA study released earlier this year also found that cheaper off-brand gas can harm engine performance in the long run.
AAA compared gasoline sold by various retailers in that study.
The study suggested that people should choose gas stations based on fuel quality rather than the price of gas, because cheaper gas can cause serious build-ups of engine deposits.
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