Premium & Unleaded Gasoline

Premium & Unleaded Gasoline

Do you know what type of fuel is right for your vehicle? Learn about octane ratings and the difference between premium and unleaded gasoline.

What Are Octane Ratings?

Knowing octane ratings is key to understanding the difference between premium and unleaded gasoline.

According to the Department of Energy (DOE), fuel contains oxygen. This oxygen helps keep gas from prematurely igniting in the engine (known as “knocking”). An octane grade or rating is based on how much oxygen is in the fuel.


What Is Unleaded Gasoline?

Unleaded gasoline is fuel with an octane rating of around 87. However, the DOE says there are three different octane ratings for fuel:

  • Unleaded Fuel: 87
  • Mid-grade Fuel: 88-90
  • Premium Fuel: 91-94

At the gas station, yellow stickers on gas pumps are required by the Federal Trade Commission (FTC) to indicate octane levels and help ensure consumers have the information they need.

How Is Premium Fuel Different From Regular Unleaded?

Premium fuel has a higher octane level compared to regular unleaded or mid-grade fuel. According to the FTC, higher octane ratings make fuel more resistant to “knocking.”

Knocking is caused when fuel prematurely combusts in one or more cylinders in the engine, says the FTC. This can lead to an audible engine knocking or pinging sound when you start your car. Consumer Reports notes that knocking could result in damage to the car’s engine over time.

While some vehicles require premium fuel, the majority of cars take regular unleaded fuel, says Consumer Reports. Using plus- or premium-grade fuels typically doesn’t affect your engine’s performance or resistance to wear-and-tear.

Remember to check your vehicle’s owner manual or ask a dealership for help to find out what kind of fuel is suitable for your car.

The Difference Between Unleaded & Premium Gas

Before breaking down the difference between gasoline brands, knowing the difference between unleaded regular and premium is the first, most important step. To explain this, a bit of combustion knowledge and chemistry is required.

Every vehicle runs through the process of combustion. During this process, the injected gasoline is ignited by a spark plug in the engine compartment. But the spark plug doesn’t fire instantly. Instead, there is a mix of air and fuel running along the spark plug, where the flame catches and expands, eventually setting the remaining air and fuel on fire. It takes some time for the literal explosion to occur.

Knock Knock . . . in Your Engine

Should any part of the air and fuel mixture fire off too soon or leak out before the flame from the spark plug ignites, it causes what is known as an “engine knock.”

This knock is a clunking sound you might hear from the engine while driving. Of course, it’s not a good sound and you want to avoid it. So, why does the engine sometimes “knock” and allow areas of the air and fuel mixture to be heated and fire off too soon? That is where the chemical aspect comes in.

What are Octane Levels?

The oil used to produce gasoline is a hydrocarbon fuel, which means individual molecules hold both carbon and hydrogen. Different kinds of fuels have different combinations of hydrocarbons. Isooctane, or “octane,” is resistant to the spontaneous exploding, so the higher the octane, the less chance there is to experience this knocking in the engine. If you look at the gas pumps at any gas station, the “Premium” fuel has a higher octane level on it. The premium octane is usually going to sit at around 91, while the regular gasoline is right around 85 to 87.

In terms of actual energy produced, including improved MPG, there is actually no real difference between unleaded and premium. Instead, a higher octane allows for more aggressive driving and a more aggressive engine. As an example, race car drivers use fuel with an octane rating often above 100, so the engine receives superior fuel that does not prematurely fire off during performance racing.

Okay, So Premium Gas is Better?

It might seem like premium is the better fuel, and in terms of octane, it is, but that doesn’t mean your vehicle should receive it. Premium levels of octane are designed for aggressive, high performance engines. Lower performance engines don’t need premium fuel, and the superior fuel generally isn’t going to do anything but waste your money. To determine whether or not your vehicle needs premium or is fine on regular, check the owner’s manual of your vehicle. If you have a performance car, such as a Corvette, Porsche, or really anything designed specifically for performance, there is a good chance premium is better for your car. Otherwise, the engine isn’t able to take advantage of the superior octane, so it does nothing but cost you more per fill-up.

Off Brand Station Gas vs. Name Brand Gas

Now that you understand the regular vs. premium aspect of fuel, you’ll have a better understanding as to whether or not an off-brand or name brand is better for your vehicle. You are going to see similar octane levels at the off-brand gas station. The regular gasoline might have an 85 octane level instead of an 87, but the occasional fill-up with this fuel isn’t going to harm your engine. The difference calculation to 100 (13 when then octane is 87) is made up of a specialized formula the gas station creates of different chemical elements designed to clean your engine. While some stations say theirs is better.