While gas prices have dropped in recent weeks, they are still substantially higher than last year. Prices range from about 26 cents to 44 cents higher per gallon of regular unleaded, depending on where you live in the U.S., according to the Energy Information Administration. Those differences can really add up and thin your wallet at a time of year when your budget is likely already stretched thin. So when it comes to choosing which octane to fill up with, it’s easy to wonder if high-octane gas is really worth the extra cost.

The simple answer to what octane rating of gasoline to use in your car is to consult your owner’s manual and use the minimum octane required, but sometimes using a high-octane gas may be a good choice.

The octane rating is a measurement of the gasoline’s ability to reduce engine knocking. Knocking, which often sounds like a rattle or a ping in the engine when accelerating, is the sound created when the compressed air-fuel mixture in the engine’s cylinders are igniting prematurely, and it can damage an engine. Premium-grade gasoline, with an octane rating of 91 or above, is designed to have the greatest resistance to engine knocking.

If you are unsure about whether you should put high-octane gas in your car, first check your owner’s manual to see the recommended octane rating for your car. Fill up with that, then drive your car and listen carefully for any sounds of knocking. If you hear knocking, then try the next-highest octane rating for a couple of fill-ups. If the sound doesn’t disappear, then pay a visit to your mechanic because your car probably needs a tuneup, a computer sensor replaced or some other repair. Once the repair is complete, you should be able to go back to using the lower octane rating.

Depending on what kind of car you drive, your owner’s manual may have a minimum octane rating as well as a recommended octane rating for your car. In these cars, fill up with the lower grade of gasoline, listen for knocking, and note if there is any decrease in performance or fuel economy. If you don’t see any differences, then continue to use the lower grade. However, as your car ages, you may find you need to shift to the recommended octane rating to prevent knocking.

While high-octane gasoline does have extra additives to prevent knocking, it won’t clean your engine better, prevent deposits or help to remove them. Federal standards require all octane grades of all gasoline brands to have detergent additives to help prevent the buildup of deposits inside an engine. So-called Top Tier Detergent Gasoline retailers have pledged to meet a set of increased standards for detergent additives. Using these brands of gasoline may improve your car’s performance or reduce engine deposits.

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If you have a car question, email it to us at Driving for Dollars. Read more Driving for Dollars columns and Bankrate auto stories. Follow her on Facebook here or on Twitter @SheDrives.

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