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You should use whatever octane is specified in your owner's manual. You will not gain any performance by using 91 octane in a vehicle that calls for 87. The only way the engine would benefit from higher octane is if the timing or compression was altered.

On the other hand, if you use lower octane in a vehicle that is supposed to use higher octane you could cause knocking and that can lead to engine damage.

Sometimes a lower octane can be used IF the manual says it is okay. My wife's PT Cruiser turbo recommends 91 but she almost always uses the cheaper 87 grade. The manual says it is okay to use it, although slightly decreased performance will result.

One final note: If you hear engine knock try the next higher octane and see if that makes it go away.

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The above reply was comprehensive. Only 10 percent of cars on the road require premium gasoline. The fact that it is called Premium is a misnomer. The octane rating has absolutely nothing to do with the actual quality of the gasoline itself. Higher compression engines do require higher octane to run at their very best. The vast majority of modern car engines however are not this kind. Check the owner's manual.


If you do have knocks you may want to try using a good fuel injector cleaner on the next couple of tankfuls. That may clear up your problem for less than 10 bucks.

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