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What does octane mean?

Octane rating is a measure of a fuel's ability to resist knocking or pinging, which happens when the air and fuel mixture ignites too early in the engine. The fuel to use is the octane rating your vehicle manufacturer requires, shown in the owner's manual.

Action level Worth checking

Why you are seeing it
It is the number on the gas pump for each grade, such as 87, 89 or 91 or higher, and it is named in many owner's manuals.
Why it matters
The grade your manufacturer requires is part of how the engine is designed to run, so using a grade below it can harm the engine over time.
What should I do?
  • Check your owner's manual for the octane rating it requires.
  • Use the grade the manufacturer requires or recommends.
  • If you want to see what a higher grade costs, the Premium vs Regular Gas Cost calculator compares the cost only.
A common misunderstanding
A higher octane number does not mean better fuel for every vehicle: for a vehicle not designed for it, higher octane gives only a minimal advantage in normal driving.

What the number measures

Octane rating is the measure of a fuel's ability to resist "knocking" or "pinging" during combustion, which is caused by the air and fuel mixture igniting prematurely in the engine. A higher octane fuel resists this better.

A simple example

What a grade costs

If regular is $3.40 a gallon and premium is $4.10, premium costs $0.70 more a gallon.

On a 12-gallon fill-up that is $8.40 more, and four fill-ups a month make $33.60 a month.

The prices are examples. Which grade to use is set by the manufacturer, not by the price.

Which grade to use

The guidance on fueleconomy.gov is to use the octane rating required for your vehicle by the manufacturer, and to check your owner's manual. The page says most vehicles are designed to run on regular, 87 octane, while some require a higher grade.

It says that using a lower octane than required can harm engine performance and damage the engine over time, and that higher octane fuel offers only a minimal advantage in normal driving for a vehicle that was not designed for it.

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