Which Type (Octane) of Gas Is Recommended for My Car?

When someone pulls up to a gas station, the first thing they’ll see is the big sign lit up with the prices for the different grades of gasoline. There’s regular, premium, super, and a number of other variations of names for these grades. But which grade is the best?

The meaning of octane

Most people think that an octane rating is to gasoline what a "proof" number is to alcohol. This is a common misconception, and the real source of the octane rating is a bit more unexpected. Octane is actually a measure of how resistant that grade of gasoline is to engine knocks at higher compression in the combustion chamber. Less stable fuel, below 90 octane, is fine for most engines. In high-performance engines though, the high compression of the air/fuel mixture may be enough to ignite the mixture before the spark plug supplies the spark. This is called a "ping" or "knock." High octane fuel is able to resist the heat and pressure of high-performance engines and avoid knocking, igniting only when the spark plug sparks.

For cars driven normally, engine knocks are easier to avoid and the higher octane does nothing to improve performance. In the past, cars would need higher octane fuel every few years due to deposits in the engine increasing compression. Now, there are cleaning detergents and chemicals in all major brands of gas that prevent this build-up. There is no reason to use a higher octane of fuel if the engine does not knock or ping.

How to identify what octane your car needs:

  • First, open the fuel filler door.

  • Next, look at the gas cap and the inside of the fuel filler door. One of these should have the recommended octane fuel for the vehicle written on it.

  • The typical way the recommended fuel octane is listed is as follows:

    • XX Octane (sometimes “AKL” is put in place of octane) recommended
    • XX Octane minimum
  • Using a fuel with an octane rating under the minimum requirement is likely to cause engine knocking.

  • Choose fuel based on the octane number, not the name (regular, premium, etc.) of the grade.

  • If the cap is yellow, then the vehicle is a flex-fuel vehicle that can take E85 ethanol.


The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

What Is Dry Gas?
Dry Dry gas is a very helpful fuel additive that is used to remove water from gasoline and prevent water-contaminated gasoline from freezing. While the solution itself is actually called dry gas, there is one brand of this fluid named...
Does Buying Good Quality Gas Matter?
Gasoline Gasoline is refined from crude oil and can contain impurities and minor inconsistencies. Because of this, it is standard practice for additives to be mixed into gas. This means that one person can fill up their car anywhere and...
What Is Dry Gas?
Dry Dry gas is a very helpful fuel additive that is used to remove water from gasoline and prevent water-contaminated gasoline from freezing. While the solution itself is actually called dry gas, there is one brand of this fluid named...

Related questions

Lost half a tank of fuel in less than 2 miles. the tank is empty. can't see a leak

I would first get a 5 gallon gas can and put it in the tank to see if gas gauge registers the fuel. Then turn on the key and listen for fuel pump operation to see if pump runs. Recheck...

The other day I had just parked and turned off my car then about 10 minutes later I went to start it and it shook and stalled

Every engine needs three things to start and run. Spark, air, and fuel. Unless the air intake is restricted, air is almost always present. If spark and/or fuel are missing, the vehicle will not run. Lack of spark can be...

What should I know about starting the engine in cold weather with E85?

If your vehicle is designed to be a flexible fuel vehicle (not all are), you may encounter some problems starting the engine in very cold weather. This is particularly true if you’re running E85. Here’s what you should know: ...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com