Gas is still expensive. “So should I spend even more for premium-grade?” a New York woman asked. “I’m willing to pay a little extra if I’ll get more miles per gallon. Will I better performance if I use premium-grade gas instead of regular-grade gas?”

No.

Octane ratings, the Federal Trade Commission explains, measure a gasoline’s ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), midgrade (usually 89 octane) and premium (usually 92 or 93). By law, the ratings must be posted on bright yellow stickers on each gasoline pump.

The recommended grade of gas for most cars is regular octane. Government regulators and petroleum industry experts say there’s no benefit in using a higher octane gasoline than your owner’s manual recommends. It won’t make your car perform better, go faster, get better mileage or run cleaner.

The American Petroleum Institute says if you find that your car runs fine on a lower grade, there is no sense switching to premium.

While most cars run on regular gas, the manufacturers of some cars with high compression engines, like sports cars and certain luxury cars, may recommend midgrade or premium gasoline. What happens if you put regular gas in a car designed for higher-grade fuel? Years ago, the car would knock, ping and even vibrate. Today, because cars have highly computerized engines, that generally doesn’t happen.

Sensors take readings and tune the engine as you drive by adjusting the engine timing for whatever fuel you put in the tank. As a result, a car that calls for the midgrade gasoline will usually run on regular without knocking. However, its performance will suffer slightly. How much? It will be about a half-second slower going from zero to 60 mph.

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