If you have ever stood at a gas pump and wondered whether your car really needs that expensive button marked “Premium,” you are not alone. Gasoline pumps offer a small menu of numbers ranging from 85 to 93 and then politely wait for you to make a decision that could cost anywhere from a few cents to a dollar or more per gallon.

Those numbers are octane ratings. They do not tell you how much energy is in the gasoline , how “powerful” the fuel is, or how clean it will make your engine. What they primarily tell you is how resistant the fuel is to knock, also called pre-detonation. And understanding that distinction can save you money.

Let’s dive into what the octane numbers actually stand for and why it’s important to know which one you should be using in your vehicle.

What Does “Octane” Actually Mean?

A gasoline-powered engine requires three things to operate: air, fuel, and spark. Air is all around us, so it’s easy to get. It enters the engine and is mixed with vaporized gasoline.…