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What is Premium GasFilling up at the gas station can be a little baffling, what with all of the options nowadays. Sometimes you’ll pull up to the pumps and see at least three options — sometimes even five or more. What makes different fuel grades special, and what makes premium, well, premium?

What Makes Premium Gas Premium?

First off, you have to know that the word premium is just marketing language. The name certainly justifies a higher price at the pump, but it doesn’t necessarily make it better, and it certainly doesn’t mean instant horsepower.

Filling your tank with it — especially if your car doesn’t require premium fuel — doesn’t make your ride run any faster or cleaner. Premium fuel’s main difference is that it contains more octane than other blends of fuel, and octane’s job is really simple: to prevent detonation.

Now, if your car had a diesel engine, detonation would be your friend because that’s how diesel engines work: by compressing the air/fuel mixture to a point where it explodes. Diesel engines are designed for this stress.

But since we’re talking about premium gasoline here, we’re talking about cars that run on gas, not diesel, and this means that the engine operates by using a spark plug to explode the air/fuel mixture at just the right moment.

The trouble is, on high-performance engines with a high compression ratio, detonation is a major risk. A higher octane rating for the fuel keeps it stable under these pressures, meaning the spark plugs ignite the air/fuel mix, not pressure.

If fuel is ignited by pressure, the engine develops a knocking sound, which means that because of detonation and early ignition, it’s essentially trying to throw itself into reverse all of the time. And that could punch a connecting rod through the oil pan, which would be bad.

Which Cars Require Premium?

Most cars that require premium fuel are of the sporting persuasion. Many of them are two-seaters, built to go fast, and don’t have a lot of luggage space. If your car is turbo or supercharged, you’ll probably need to fuel it with premium. Consult your owner’s manual for the specifics.

Differences Between Premium and Regular Unleaded

The main difference between most regular unleaded fuel blends and their so-called premium counterparts is their octane ratings.

Regular unleaded usually carries an octane rating of 86 or 87, while premium grades are usually rated at 91 or more.

The middle grade, normally rated at somewhere around 89, is just a huge waste of money — because no cars are designed to use it. All you’re buying is more octane, which only inhibits knock (detonation). Octane does not equal horsepower. If your car was built for regular unleaded, use regular unleaded.

The Risks of Using the Wrong Grade

If your car was built for premium, but you use regular unleaded instead, you’ll destroy your engine through detonation. Play it safe and stick to the fuel recommended by the manufacturer.