Unleaded Gas: Everything You Need to Know

Gassing up at fuel stations is a necessity for drivers, whether part of a weekly commute or on the way to weekend fun. As liquid gold pumps into the tank, most people don’t give much thought to what’s in it. What is unleaded gas? And what do different grades really mean at the pump?

What is unleaded gas?

Unleaded gas doesn’t contain any lead additives. As of 2021, the chemical is no longer found in gasoline intended for on-road vehicle consumption in the United States as well as the rest of the world.

Beginning in 1921, producers first added lead to gasoline as a way to eliminate engine knock. Adding tetraethyl lead to fuel provides octane to gasoline. In simple terms, octane makes fuel more stable so it doesn’t combust prematurely in the engine. Lead also acts as a lubricant, reducing friction in the combustion chamber that helps improve fuel mileage and reduce wear and tear.

Regulations on unleaded gas

It was known that lead was not safe, even in small quantities. Lead is harmful to childhood development, increases rates of behavioral disorders and contributes to lifelong health concerns. It took more than 50 years for governments to police lead usage, and some say that intervention wasn’t because of illnesses at all.

Despite the risks, lead wasn’t phased out of gasoline until the passage of the Clean Air Act. Lead contaminated the newly introduced catalytic converters, which were intended to reduce greenhouse gas emissions. Unleaded fuel options became the norm. Over the next two decades, leaded gas became uncommon outside of small markets overseas, then eliminated altogether.

Is unleaded gas “regular gas?” Yes. When you drive to any fuel station, you won’t find a pump that mentions leaded gas anymore, so saying “regular unleaded gasoline” is redundant. To boost octane, modern gas instead uses ethanol.

What is octane?

Octane is a rating system that measures how stable fuel is. The higher the octane rating, the more stable the fuel is against auto-ignition. When the air-fuel mixture is compressed in an engine cylinder, a less-stable fuel may spontaneously combust, pushing the cylinder downward against the upward path it’s traveling. Higher combustion engines need more octane to protect against this.

The scale uses iso-octane as the reference point for the best resistance to auto-ignition among octanes with a rating of 100, and heptane is the most volatile with a rating of zero. Two testing methods, Research Octane Number and Motor Octane Number, are averaged to get the octane rating you see on the pump.

That means that the higher the octane number at the pump, the more the fuel can resist unintended combustion in the engine.

What is premium gas?

Gas products with an octane rating greater than 90 are considered premium. There used to be premium leaded gas, which just meant there was more lead in the fuel to increase the octane rating, but now all premium gas is lead-free. Premium gas is typically more refined and contains additives to reduce engine wear and reduce friction between metal surfaces.

Why does premium gas cost more?

Is charging more for higher fuel grades just a money grab? Some people might think so, especially because ethanol is blended with almost all gas grades today to boost octane. However, ethanol burns faster than regular gasoline and doesn’t contain as much energy, so simply adding more ethanol isn’t beneficial.

The base octane rating prior to adding ethanol is higher in premium gas, and that costs more to produce. And because consumers aren’t given production cost breakdowns, there’s always room to speculate that part of the extra cost is just because gas stations and producers can charge more.

Premium vs regular gas

Does your car need premium gas? The answer is behind the fuel door. When it’s open, you’ll see a label either on the door or by the gas cap. If it says “PREMIUM FUEL REQUIRED,” your car needs premium to operate at full performance. If it says “PREMIUM FUEL RECOMMENDED,” you can switch back and forth between regular unleaded gas and premium with minimal performance effect or none at all.

High-compression and high-efficiency engines require premium fuel, like the kind you find in a luxury car or one equipped with a turbo.

But if there isn’t an indication you need premium gas, there’s a good chance you’re spending extra money at the pump with no benefit.