Premium. Mid-Grade. Regular.

About every week or two, those who drive a car are faced with a choice – premium, mid-grade, or regular. I'm talking, of course, about gasoline and if you don't know what the difference between them is, other than about $0.50 per gallon, then you're probably not a gear head. That's okay, though, because we're about to explain why premium gas is worth it for some and totally not worth it for others.

But first, there's something you have to understand: Octane. Contrary to popular belief (outside of the car world), a higher octane fuel (premium) is actually more resistant to ignite, meaning it is less likely to combust until it reaches a higher temperature. Lower octane fuel, like a mid-grade or a regular-grade fuel, is the opposite – it's easier to combust and will do so at a lower temperature.

So why does this matter? 

Well, if you have a high-performance vehicle then the engine is likely engineered to rev to high rpms, have tighter clearances in the combustion chamber, or use a turbo/supercharger to force a lot of air (and therefore, create more pressure and heat) into the combustion chamber. That means it's absolutely critical (especially with a lot of fast moving parts) that the fuel detonates at the exact right time – hence using a higher octane fuel or a fuel that resists combusting until a certain temperature.

If the fuel does combust before intended, e.g. before the spark plug fires (called knock or ping), and over time can damage your engine and leave you with a boat anchor under the hood. 

If you have a normal vehicle, you're not going to hurt your car by putting premium in it, but it's not really worth it as it's not going to perform any differently, and you're probably not going to get better fuel mileage. Lower performance engines create less power, less pressure, and less heat in the combustion chamber so they need less octane to operate properly.

As always, it's best to check your owners manual. Some "normal" cars run surprisingly tight clearances – like the Mazda3, which requires at least 87-octane or else you could damage your emission control system or engine knock could occur. Don't listen to the dealer who says you don't need it, listen to the engineers. 

With that said, modern cars are equipped with knock sensors and can compensate – to some extent – for lower octane fuels by using this sensor to alter the fuel table and ignition timing of the engine. In other words, if somebody accidentally puts mid-grade or regular in your car, it'll most likely be fine, just keep your foot out of it when you drive it or add an octane booster.

But we don't recommend doing it repeatedly or over long periods of time. So yes, premium gas is worth the premium if your owner's manual says so. 

What are your thoughts? Any mechanics or engineers have anything to add? If so, let us know in the comments below!

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