Why are there so many gas choices?

Ryan Meyer, Energy Procurement Specialist

Have you ever sat pumping gas and wondered why there are so many types of gasoline? Have you wondered whether the more expensive gas gets more miles per gallon? Will the lower price gas hurt your engine? Take a few minutes to learn more about your options!

Gasoline varies by grade

There are three main grades of gasoline at most retail gasoline stations:

• Regular (the lowest octane fuel–generally 87)

• Midgrade (the middle-range octane fuel–generally 89–90)

• Premium (the highest-octane fuel–generally 91–94)

Some companies have different names for these grades of gasoline, such as regular, unleaded, mid-grade, medium, super, premium, or super premium, but they all indicate the octane rating, which is the antiknock property of gasoline. Anti-knock prevents detonation in the combustion process of a combustion engine.

What is Octane?

Octane ratings are measures of fuel stability. These ratings are based on the pressure at which a fuel will spontaneously combust (auto-ignite) in a testing engine. The octane number is the simple average of two different octane rating methods - motor octane rating (MOR) and research octane rating (RON) - that differ primarily in the specifics of the operating conditions. The higher an octane number, the more stable the fuel.

How does the octane level affect my vehicle?

Engines are built for controlled combustion, where a spark ignites the fuel and it burns smoothly. However, if unburned fuel ignites from heat and pressure instead of the spark called “knock” or “detonation” it causes uneven pressure and can damage the engine. Modern engines use sensors and computers to detect and adjust for knock by delaying the spark, which protects the engine but can reduce efficiency. Another issue, pre-ignition, happens when fuel ignites too early. Engine computers also try to prevent this, though it can have an impact on the economy and emissions. See the picture below to illustrate.

So, will my car blow up if I put the wrong grade gas in my vehicle?

Using the wrong grade of gasoline occasionally usually won’t hurt your car, but here’s what to keep in mind:

• If your car needs regular gas (87), using premium won’t give you extra power or mileage, it just costs more.

• If your car recommends premium, you can use regular gas (87) in a pinch, but you might notice less performance or fuel efficiency.

• If your car requires premium, using regular gas (87) can lead to engine knocking and long-term damage. Always stick to premium in this case!

Best tip: Check your owner’s manual and use the gas your car was built for. That’s how you get the best performance and keep your engine healthy.

Stay tuned! In a future post, we'll dive into why 88 Octane fuel has become more popular in the past couple of years.