More than 16 million drivers are calculated to be spending extra money to fill up with premium fuel, even when their car doesn’t require it, according to a new study by AAA. Further, AAA testing found that vehicles designed to run on regular gas did not show any emissions, fuel economy, or horsepower improvement when using premium fuel.

Earlier in the year, Consumer Reports investigated this concept by evaluating two models that come with premium-fuel recommendations: the 2015 Acura TLX four-cylinder and the 2016 Nissan Maxima V6. Likewise, we found no difference in fuel economy when tested with regular and premium fuel. During testing, the cars felt and sounded the same; we did not experience any engine pinging or knocking noise in either car when using regular fuel. Likewise, 0-to-60 mph acceleration times were identical in the TLX and Maxima on regular and premium gasoline.

The AAA testing was conducted with a dynamometer equipped with emissions test equipment using a four-cylinder Mazda3, a Dodge Charger V6, and a Toyota Tundra with a V8.

Although the methodologies differ, both organizations have come to the same conclusion: Upgrading fuel isn’t worth the money.  

Based on a survey of more than 1,000 car owners, AAA estimates that motorists may be spending more than $2.1 billion per year unnecessarily by upgrading to premium fuel. AAA asserts that consumers have come to associate “premium” with better performance; perhaps they're confused because cars requiring premium often deliver high performance—due to their engine, not the fuel.

Drivers looking to treat their engine to the best fuel to aid its operation would be well served by choosing a Top Tier gas, based on previous AAA study. Top Tier gas designates fuel from a wide range of brands; it goes beyond the minimum standard for detergent additives to better protect engines from carbon buildup and deposits on the intake valves. Such buildups can result in a rough idle, acceleration hesitation, knocking/pinging, and reduced fuel economy.

Top Tier retailers include 76, Aloha Petroleum, Amoco, Arco, Beacon, BP, Break Time, Cenex, Chevron, Citgo, Conoco, Co-op, Costco, CountryMark, Diamond Shamrock, Entec, Esso, Express, Exxon, Holiday, Kwik Star Stores, Kwik Trip, Mahalo, MFA, Mobil, Ohana Fuels, Petro-Canada, Phillips 66, Puma, QT, Quik Trip, Road Ranger, Shamrock, Shell/Shell V-Power, Sinclair Standard, SuperAmerica, SuperFuels, Tempo, Texaco, Tri-Par, and Valero.

Bottom line. Follow the automaker’s guidelines for fuel, found in the owner’s manual and inside the fuel filler door. Most cars are designed to run on regular, 87-octane fuel. Only about 16 percent of vehicles require premium, according to AAA. For those models for which premium is recommended—not required—again, save your money and choose regular.