If you drive a BMW from us, you probably want to know the best type of fuel to be putting into your vehicle. We get it, it’s important. The right fuel can keep your engine going for years to come, and keep it going efficiently to boot. So, here’s a little primer on the types of gasoline you might see at the pump, and exactly what those numbers mean.

The difference between fuel types is actually pretty scientific. The numbers on the pumps actually indicate the octane levels of the gasoline, which can make a difference in the performance of your engine. What do we mean by octane? Here comes the science – the oil used in gasoline production is a “hydrocarbon fuel,” so the individual molecules hold both carbon and hydrogen atoms. Different types of fuels have different numbers of hydrocarbons, one of which is isooctane (what we just shorten to “octane”). This molecule is resistant to spontaneous explosion, which makes it more efficient in your engine. A higher level of octane won’t help your MPG – that’s something you can only change by careful driving – but it will help your engine’s performance when driving.

The way your engine works, for those of you who might not be familiar, is that the gasoline is injected into the cylinders of your engine, compressed, and then the gas is ignited by the spark plugs. So, you can see why the ignition resistance provided by the octane is so important! If the octane level is lower, there’s a higher chance that the gasoline will ignite before it’s supposed to, which creates a “knock” in your engine. That sound means that you should probably be using a higher octane fuel in your engine.

A caveat, however: not all engines are created equal. Some engines, like those in some models of BMW, are made for a higher level of performance and therefore require a higher octane fuel. Some engines don’t need this higher octane, and to get it at the pump would be a waste of your money. However, if you do have a high-performance engine, purchasing the higher octane – or premium, if you prefer – fuel will allow your vehicle to perform at its highest level. Racecar drivers usually use fuel with an octane level of 100 or higher for ultimate performance on the racetrack.

You might not be racing in Formula One, but BMWs are designed for a higher level of performance. Knowing what type of fuel to put into your tank is just one step to knowing how to reach your vehicle’s fullest potential.