We frequently are asked this question or similar ones about the best fuel to use, and with pump prices rising, it bears repeating that premium gas yields higher fuel economy only if the engine in your car requires premium gasoline. If an engine is designed for premium gas (90 pump octane or higher), using a lower-octane fuel will cause the engine’s computer to adjust ignition timing to compensate, resulting in less power and lower fuel economy. You may also experience engine “pinging” or knocking, which sounds like marbles rolling around in a can.


However, if premium gas is only recommended for your engine, then you may not notice any loss in fuel economy or only a small amount. Some car owners have told us they don’t see a difference in economy or performance, though others report more sluggish performance or even mild pinging.

If your engine is designed to run on regular gas (87 pump octane), engineers insist there is no significant benefit to using midlevel (around 89 octane) or premium gas with higher octane ratings. There are some who claim their engines run better on premium, but that is probably part placebo effect and partly to justify spending 20 cents or more per gallon. The American Petroleum Institute says any fuel economy gains will be difficult to detect in daily driving.

You should use the type of gas that the manufacturer recommends for your engine. Most vehicles have a sticker mounted on the fuel door or gas cap, and all owner’s manuals specify which fuel to use (usually with warnings of the potential consequences if you don’t).

You can learn more about motor fuels in the Cars.com Advice section.

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Answered by Rick Popely on March 6, 2012 in How Does That Work? | Permalink

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