Difference Between 87 and 91 Octane Gas

Comparisons, Knowledgebase

Last Updated on November 25, 2022 by mdmtool

The gas you put into your car can significantly impact how well your vehicle runs. Gasoline comes in different grades or octanes; each degree is designed for another purpose. The two most common grades of gasoline are 87 and 91 octane. There are many differences between 87 and 91 octane gas and what each is best used for.

What Is 87 Octane Gas?

what is 87 Octane

87 octane gas is a fuel mixture that contains 87% octane and 13% other hydrocarbons. It is the most common gasoline used in cars, trucks, and SUVs.

What Is 91 Octane Gas?

what is 91 octane gas

91 octane gas is a fuel mixture that contains 91% octane and 9% other hydrocarbons. It is typically used in high-performance vehicles that require premium fuel.

Difference Between 87 Octane And 91 Octane Gas

Octane Rating Of 87 And 91 Octane Gas: The octane rating measures a fuel’s ability to resist “knocking” or “pinging” during combustion. The higher the octane rating, the higher the quality of the fuel. In the United States, unleaded gasoline typically has octane ratings of 87.

Performance: 91 octane gas provides better performance than 87 octane gas.

Ignition: 91 octane gas has a higher ignition point than 87 octane gas. It will take longer for the fuel to ignite, leading to improved engine performance.

Burning: 87-octane gas burns faster than 91-octane gas. The lower the octane rating, the higher the risk of knocking.

Emissions: 87 octane gas produces fewer emissions than 91 octane gas.

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Detonation: 91 octane gas is less likely to cause Detonation than 87 octane gas. This will not cause the engine to “knock” or “ping” quickly, leading to improved engine performance.

Volatility: 87 octane gas is less volatile than 91 octane gas. It will evaporate more slowly and will not easily ignite. 91 octane gas is more volatile than 87 octane gas. And will evaporate more quickly and will easily ignite.

Compression: 87-octane gas has a lower compression ratio than 91-octane gas. It will compress less in the engine, leading to improved engine performance.

91 octane gas has a higher compression ratio and will compress more, leading to increased engine power.

Efficiency: 87-octane gas is less efficient than 91-octane gas. It’s because 87-octane gas contains less octane and more other hydrocarbons.

Cost: 87 octane gas is typically cheaper than 91 octane gas. 

Availability: 87 octane gas is widely available at most gas stations.91 octane gas may not be available at all gas stations but is typically available at gas stations that sell premium fuel.

87 Octane

“Premium” Gas May Vary By State

The difference between 87 and 91 octane gasoline is not only 3-grades on the octane rating but the actual difference in chemical composition can vary significantly depending on where you live.

Most states use a “head-blending” system to produce gasoline. This means that the final octane rating of the gas is determined by mixing different “pools” of gas with different octane ratings. The actual composition of each pool can vary depending on the time of year and the refinery’s location.

For example, refineries might use heavier crude oil to produce gasoline in winter. This crude oil has a higher natural octane rating, so the final gas will also have a higher octane rating.

Or, if a refinery is located near an area with a lot of natural gas production, they may use “reformed” natural gas in their gasoline blend. Reformed natural gas has a very high octane rating, which will also raise the final octane rating of the gasoline.

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So, while the octane rating of gas may be the same from state to state, the actual composition can vary quite a bit. Some car owners notice a difference in performance when they drive across state lines.


What Is Detonation Knock?

Detonation knock is a knocking noise you’ll hear when the air-fuel mixture in the cylinders is detonating more than one place at a time. Parts of the air/fuel mixture can start to ignite too early. When these mini fireballs collide, they create a knocking noise.

How Does Octane Rating Affect Knocking?

The higher the octane rating, the less likely the fuel is to knock. That’s because a higher octane fuel resists igniting in more than one place at a time.

When Should You Get 91 Octane Gas?

If your car has a high compression ratio or requires premium fuel, you’ll need to get 91 octane gas. High-performance vehicles usually have a higher compression ratio and thus require premium fuel. Check your car’s owner’s manual to see what fuel it needs.

Why Do Some Cars Require Premium Gasoline?

Cars with high compression ratios or turbochargers require premium gasoline because their engines produce more heat. If you use regular gasoline in one of these cars, the fuel is more likely to detonate prematurely. This can damage the engine.

Can I Use A Higher Octane Fuel Than My Car Requires?

Yes, you can use a higher octane fuel than your car requires. However, it’s unnecessary and won’t improve your car’s performance. It might even damage your engine.

Why Is 87-Octane Gas More Widely Used Than 91-Octane Gas?

87-octane gasoline is more widely used than 91-octane gas because it’s the most common type of gasoline and it’s also the cheapest.

What Are The Expected Damages To A Car From Putting 87 Octane Gas When 91 Octanes Is Recommended?

Using 87-octane gasoline when your car requires 91-octane gasoline can damage your engine. The lower octane fuel also doesn’t resist Detonation, so it’s more likely to cause knocking. This knocking can damage the engine over time.


Well, the main difference is in the octane rating. The higher the octane rating, the more resistant the fuel is to knocking or pinging during combustion. However, using a higher octane fuel than recommended for your car’s engine will not benefit you. It may hurt performance and cause problems. So, you’re wasting your money if you’re using 91-octane gasoline in a machine that only requires 87-octane. It is important to go by the fuel requirement of your vehicle.


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