What octane rating means

Octane rating measures a fuel's ability to resist knocking or pinging during combustion, caused by the air/fuel mixture detonating prematurely in the engine. In the U.S., unleaded gasoline typically comes in three grades, shown in large black numbers on a yellow background on the pump:

From Selecting the Right Octane Fuel (fueleconomy.gov), read November 9, 2026.

Gasoline rated 85 octane is sold in some high-elevation areas. Fueleconomy.gov says that unless you have an older vehicle with a carbureted engine, you should use the manufacturer-recommended fuel even where 85 is available.

Which fuel should you use?

Use the octane rating your manufacturer requires; check your owner's manual. Most gasoline vehicles are designed for 87 octane, but some are designed for higher octane fuel.

Manufacturers often require or recommend higher octane fuel for engines with a higher compression ratio or with supercharging or turbocharging. In those engines, fueleconomy.gov says high octane fuel improves performance and fuel economy.

Using lower octane than required can cause the engine to run poorly, can damage the engine and emissions control system over time, and may void your warranty. Older vehicles may knock or ping; many newer vehicles adjust spark timing to reduce knock, but power and fuel economy still suffer.

From Selecting the Right Octane Fuel (fueleconomy.gov), read November 9, 2026.

Is premium gas worth it?

If your vehicle requires midgrade or premium fuel, fueleconomy.gov says it is absolutely worth it. If your owner's manual says premium is not required but the car will run better on higher octane, it is up to you; the cost increase is typically higher than the fuel savings.

For most vehicles, higher octane may slightly improve performance and gas mileage during severe duty, such as towing a trailer or carrying heavy loads, especially in hot weather. Under normal driving conditions, you may get little to no benefit. Higher octane fuel costs more because the components that boost octane are generally more expensive to produce.

Ethanol has a much higher octane rating (about 109) than gasoline, and refiners blend it in to boost octane; most U.S. gasoline contains up to 10% ethanol.

From Selecting the Right Octane Fuel (fueleconomy.gov), read November 9, 2026.

Service at Elgin Auto Sales & Service Center

Check engine light on, or due for an oil change or a tire check? Schedule service or see our service specials.

Our service department at 1200 E. Chicago St. in Elgin is open Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m., and is closed Sunday. Get directions.