When we think of gasoline, we usually think of it in terms of “leaded” or “unleaded,” but if you think about it, we never see gasoline that’s not labeled as unleaded anymore. Sure, we have the “regular,” “premium,” and “plus” (or related nomenclature) but it’s never referred to as anything but unleaded. Why is this? Why do we think of gasoline in those terms, even though we don’t have any context for referring to gasoline as leaded at all? Read on to find out!

So, there was such a thing as leaded gasoline. This literally means that lead (specifically Tetraethyl lead) was added to gasoline in order to increase the octane rating of the fuel. The octane rating simply means that the fuel can be compressed by the car engine’s cylinders even more – which means that more power comes out of each drop of fuel. When fuel is compressed, it will ignite due to friction. With a higher octane rating, the fuel won’t ignite as soon, so it can be compressed even more. The lead was added to increase this in the early 1920’s. Before the advent of leaded fuel, almost every car engine had a knock. This was the fuel igniting before it was supposed to because it had been compressed past its ignition point and ignited before it was really supposed to. With the addition of lead, this didn’t happen, and the knock was silenced. However, lead is an incredibly toxic substance for humans. As a natural heavy metal, it doesn’t decompose at all – it just stays. And because humans are who deal with cars and gasoline, the lead stayed in skin, muscle, and bone and caused lead poisoning and death. So, in the 1970’s, leaded gasoline began to be phased out and was banned completely in all vehicles across the United States in 1995. Now, since the ban on leaded gasoline, the average level of lead in the blood of people living in the U.S. has decreased by over 75%. That’s a lot!

So, the difference between regular and premium fuel today is still that octane level. Different types of car engines require different octane levels in the fuel they need, based on the engine’s performance and how much power it needs to run. However, these days the octane level isn’t increased by lead – thanks, modern technology! – so you can feel better about using premium fuel. If you don’t have a high-performance engine, though, don’t waste your money on the fuel. It won’t make your engine magically into that of a race car, it’ll just be pointlessly more expensive gas. If you DO have a high-performance engine, though, go ahead and fill up with that 92 – since there’s no lead, you’re all set.