U.S. drivers have "wasted" more than $2.1 billion in the last year using premium-grade gasoline in vehicles designed to run on regular fuel, according to research by the American Automobile Association (AAA).

According to AAA, over the past year 16.5 million U.S. drivers have put premium fuel in a vehicle in which the manufacturer’s recommendation is to use regular fuel. After using industry-standard test protocols designed to evaluate vehicle performance, fuel economy and emissions, the association found no benefit to using premium gasoline in a vehicle that requires only regular-grade fuel.

According to AAA, over the past year 16.5 million U.S. drivers have put premium fuel in a vehicle in which the manufacturer’s recommendation is to use regular fuel. Image credit: Pixabay. “Drivers see the ‘premium’ name at the pump and may assume the fuel is better for their vehicle,” says John Nielsen, AAA’s managing director of automotive engineering and repair. “AAA cautions drivers that premium gasoline is higher octane, not higher quality, and urges drivers to follow the owner’s manual recommendations for their vehicle’s fuel.”

In partnership with the Automobile Club of Southern California’s Automotive Research Center, AAA tested 87-octane (regular) and 93-octane (premium) gasoline in vehicles equipped with a V-8, V-6 or I-4 engine designed to operate on regular-grade fuel. To evaluate the effects of using a higher-octane fuel when it is not required by the manufacturer, each vehicle was tested on a dynamometer—essentially a treadmill for cars that is designed to measure horsepower, fuel economy and tailpipe emissions when using both fuel types under a variety of driving conditions.

The laboratory tests found no significant increases in any tested category, indicating the practice of using premium gasoline when it is not required for the vehicle offers no advantage.

“When it comes to gasoline, ‘premium’ does not mean ‘better’ if your vehicle doesn’t require it,” says Nielsen. “Drivers looking to upgrade to a higher-quality fuel for their vehicle should save their money and select a Top Tier gasoline, not a higher-octane one.”

Previous AAA research found that fuel quality varies significantly among gasoline retailers and that using a gasoline that meets so-called Top Tier standards can result in 19 times fewer engine deposits, increased vehicle performance and improved fuel economy. Top Tier Detergent Gasoline—available in both regular and premium—is a performance specification supported by eight global automakers: BMW, General Motors, Fiat Chrysler Automobiles, Honda, Toyota, Volkswagen, Mercedes-Benz and Audi.