Although it’s exciting to see the recent development of electric vehicles and other fuel sources for personal vehicles by companies like Tesla and even General Motors, the majority of us will still be driving vehicles powered by the internal combustion engine for the foreseeable future. This leads to a question many have had for decades – “Which grade of gasoline should we be using?”

If you have visited any mainstream gas station, you have undoubtedly given the following fuel grade options (besides diesel fuel which is another story):

87 octane

89 octane

91 octane

94 octane (available at certain gas retailers)

I will go into greater detail below – but here’s the quick answer. If your car was built in the last fifteen years, you should only be using the fuel grade recommended by the manufacturer. This information can be found in the owner’s manual or sometimes it can be found on the inside of the gas lid or online.

What’s The Difference?

The difference is that premium gas is less combustible. It has a higher percentage of octane (for example, 89%, 90%, or 91%) which is resistant to combustion, and less heptane, which is much more likely to ignite when compressed, according to How Stuff Works.

So Which Gas Should I Use?

You should only be using the fuel recommended by your manufacturer. You can find this information in your owner’s manual, or the US Department of Energy has a handy guide to help you figure it out. 

What If I Use Cheap Gas in a Premium Car?

If you are lucky enough to be driving a premium car with a premium engine that recommends premium gas, then don’t cheat yourself by using cheap gas. If you do choose to use the wrong grade, modern engines are able to adjust their compression to accommodate so you are unlikely to cause any major damage. However, you will be sacrificing power and fuel economy, making the vehicle less efficient, and potentially erasing any cost benefit. You may also experience some engine knocking. Plus you spent a lot of money on a premium car, so why not enjoy it to its full potential?

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