10 Things You Should Know About Gasoline

Premium gas doesn't provide any more power or contain better additives than regular gas, and it contains the same amount of ethanol as other grades. It just resists detonation (knock) better than lower-octane gas—nothing more, nothing less.

Some brands place slightly more detergent additive in their premium than in their other grades, but all grades meet the minimum required by the EPA. Bottom line? The carmaker knows best, so use the octane-rated fuel that's called for in your owner's manual. If your engine requires or 'recommends' 89- or 93-octane fuel, that's what you should use to get peak performance and fuel efficiency. But there is an exception to the rule.

If you have an older car that's designed for 87-octane gas and it knocks when you punch the pedal, try filling it with 89-octane fuel to see if the knock goes away. If so, keep using 89-octane to regain some power and save your engine.

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