Last year AAA reported that Americans waste billions of dollars each year on premium gasoline. A new AAA study concludes that’s true in most cases even if premium-grade is recommended for your car.

If you are like many Americans, you may occasionally treat your car to premium gasoline. You might not be certain whether it helps, but it can’t hurt, right? Maybe not, but you just might be throwing money down the drain.

Last year I reported on a study by AAA that concluded American drivers had wasted more than $2.1 billion during the previous year by using premium-grade gasoline in vehicles designed to run on regular fuel. Now AAA has released new research findings that tested vehicles for which premium-grade gasoline was recommended but not required.

Together with the Automobile Club of Southern California’s Automotive Research Center, AAA tested vehicles that recommend the use of premium (91 octane or higher) gasoline. These vehicles were tested under extreme driving scenarios such as towing, hauling cargo and aggressive acceleration. AAA’s tests under these conditions showed:

• Fuel economy for test vehicles averaged a 2.7% improvement. Individual vehicle test result averages ranged from a decrease of 1% (2016 Audi A3) to an improvement of 7.1% (2016 Cadillac Escalade).
• Horsepower for test vehicles averaged an increase of 1.4%. Individual vehicle test result averages ranged from a decrease of 0.3% (2016 Jeep Renegade) to an improvement of 3.2% (2017 Ford Mustang).
• According to national averages, the price difference between regular and premium gasoline is approximately 20% to 25% — about $0.50 per gallon.

AAA concluded that the vehicles tested are unlikely to see any benefit from using premium gasoline during typical city or highway driving. But even if someone consistently drives under the extreme scenarios tested, a 2.7% fuel economy improvement won’t justify paying 25% more for premium gasoline. Thus, the conclusion is the same as the conclusion from last year’s research — Americans are mostly wasting their money if they are buying premium in this situations.

Of course, if a vehicle requires premium, that’s a different matter. Higher-octane fuels are more resistant to pre-ignition, which allows them to be used in engines with higher compression ratios. That enables higher performance and higher fuel efficiency than in engines with lower compression ratios. Using a lower-grade fuel in such an engine can result in knocking and pinging as the fuel ignites too early, and this can damage the engine.

Note that premium gasoline doesn’t necessarily contain any more energy or any better additives than cheaper gasoline. So unless you have a vehicle that requires premium gasoline, you are probably wasting your money if you are buying it. AAA’s newest research shows that’s true even if premium fuel is recommended for the vehicle. But if you switch to regular and notice an engine knock, then you should probably stick with premium.

Additional Resources

• Full Report: AAA Premium Fuel Research, Phase II
• Fact Sheet: AAA Premium Fuel Research, Phase II