AAA: Premium gas not worth the money for most cars

If you're buying premium gasoline for a car that doesn't require it, you may be wasting your money, according to AAA.

The drivers organization tested six cars where manufacturers recommend -- but don't require -- premium gasoline (rated as 91 octane or higher) and found that premium fuel had a slight benefit in "extreme driving scenarios," like towing or cargo hauling. Fuel economy improved by an average of only 2.7 percent when they used premium gas, while horsepower increased a meager 1.4 percent on average. 

The tested cars were the Audi A3, Cadillac Escalade, Ford F150, Ford Mustang, Jeep Renegade and Mazda Miata.  

Because premium fuel costs as much as 25 percent more than regular, the increased performance may not be worth it, AAA said. 

"The modest fuel economy improvements found in AAA tests do not offset the higher cost of premium gasoline," AAA said in a statement.

Some 1.5 million cars and trucks were sold in the U.S. last year that advise motorists to use premium gas. Engines have to be calibrated to actually require high-octane fuel in order to benefit from it, according to John Nielsen, AAA's managing director of automotive engineering and repair.

"Based on AAA's testing, vehicles that only recommend premium gasoline can't take full advantage of higher octane fuel and, as a result, the benefit that comes from upgrading to premium gasoline may not offset its high cost," Nielsen said.