What Octane Means for Gasoline—and How to Pick the Right Grade

Octane is a measure of gasoline’s resistance to engine “knock” (uncontrolled combustion); it does not indicate fuel quality or energy content. Use the octane grade your vehicle’s manufacturer specifies; higher octane generally helps only engines designed or tuned for it, such as many turbocharged or high-compression models.

What “octane” actually measures

In spark-ignition engines, fuel-air mixtures can sometimes ignite prematurely or burn unevenly under high pressure and heat, creating knock (also called pinging). Octane ratings quantify a fuel’s ability to resist this. The rating compares the fuel to laboratory blends of iso‑octane (high knock resistance) and n‑heptane (low knock resistance). A fuel with an octane number of 90 behaves like a mixture that’s 90% iso‑octane and 10% n‑heptane in terms of knock resistance.

There are several ways octane is expressed, and understanding the label you see helps you choose correctly.

• RON (Research Octane Number): Measured under relatively mild conditions; common on pumps in Europe and many other regions.
• MON (Motor Octane Number): Measured under more severe conditions (higher speed/temperature); typically lower than RON for the same fuel.
• AKI or (R+M)/2: The average of RON and MON used on U.S. and Canadian pumps. AKI 87 (regular) roughly corresponds to RON 91–92.

In practice, U.S. pump numbers are AKI; European numbers are RON and appear about 4–6 points higher for the same fuel.

What you see at the pump

Most stations offer three grades and may display additional fuel information such as ethanol content and detergent standards. Labels vary by region, but the core ideas are consistent.

• Regular: 87 AKI (about 91–92 RON).
• Midgrade: 88–90 AKI (roughly 93–95 RON).
• Premium: 91 or 93 AKI (about 95–98 RON), depending on the region.
• Labeling: U.S. pumps typically read “Minimum Octane Rating (R+M)/2.”
• Ethanol blends: E10 (up to 10% ethanol) is common; E15 is approved for most 2001+ vehicles but check your manual; E85 (51–83% ethanol) has very high octane but lower energy per gallon and is only for flex-fuel vehicles.
• Detergents: “Top Tier” is a detergent standard endorsed by many automakers; it’s about cleanliness, not octane.
• High altitude note: Some Mountain West areas sell 85 AKI “regular.” Many modern vehicles are not calibrated for 85; manufacturers often still recommend 87 AKI even at altitude.

If in doubt, follow the octane grade listed in your owner’s manual or on the fuel door. The posted number tells you knock resistance, not how “strong” the gasoline is.

When higher octane matters

Higher octane allows engines to run more spark advance or higher compression without knock, which can unlock performance in engines designed for it. For others, it offers little or no benefit.

• Required: Many turbocharged, supercharged, or high-compression engines specify 91+ AKI. Using lower than required can reduce power, trigger knock control, and in extreme cases risk engine damage.
• Recommended: Some vehicles say “premium recommended.” They can run on 87–89 AKI, but you may see reduced acceleration or slightly worse fuel economy in hot weather or under heavy load.
• Heavy load and heat: Towing, mountain climbs, or heat waves increase knock tendency. Stepping up one grade can help if your engine audibly pings or the manual suggests it.
• Carbon buildup or older engines: Deposits can raise effective compression. A higher octane may quiet knock, but the better fix is cleaning or maintenance.

If your vehicle is tuned for premium, it will typically advertise peak power/MPG on that grade. Otherwise, higher octane is usually unnecessary.

What octane won’t do

Octane is often misunderstood. Here’s what it does not guarantee.

• Not more energy: Octane rating isn’t a measure of energy content. Premium doesn’t inherently give better fuel economy.
• Not automatic power gains: Engines not designed for high octane rarely make more power just because you use it; modern ECUs already optimize timing for the grade.
• Not cleaner fuel: Cleanliness depends on detergents (e.g., Top Tier), not octane.
• Not a cure-all: Octane resists knock/detonation; it doesn’t fix pre-ignition, mechanical issues, or poor-quality fuel.

Think of octane as compatibility with your engine’s compression and tuning—not an overall quality score.

Practical guidance: choosing octane

Use these steps to match fuel to your vehicle and conditions.

1. Check the owner’s manual and fuel-door label for “Required” or “Recommended” octane. “Required” means don’t go lower.
2. Use 87 AKI in most vehicles unless specified otherwise; use 91/93 AKI in engines that require premium.
3. If premium is “recommended,” you can try regular. If you notice knocking, reduced performance, or the manual cautions for hot weather/towing, step up a grade.
4. Avoid 85 AKI at altitude unless your manual explicitly allows it; many modern engines expect 87 AKI even in the mountains.
5. Don’t conflate ethanol and octane: ethanol raises octane but lowers energy per gallon. Use only the ethanol level your vehicle approves.

Following manufacturer guidance protects performance and warranty, and usually saves money at the pump.

Special cases and quick facts

Ethanol and octane

Ethanol has a high octane rating, which is why E85 supports aggressive turbo tuning in flex-fuel or dedicated setups. But because ethanol contains less energy per gallon than pure gasoline, mileage drops with higher ethanol content. For non–flex-fuel vehicles, stick to E10 (or E15 if your manual approves).

Modern knock sensors

Most engines use knock sensors and adaptive timing. On lower octane than ideal, they retard timing to protect the engine, which can reduce power and occasionally fuel economy. That doesn’t mean damage—unless you’re running below the “required” rating.

Small engines and power equipment

Many mowers, generators, and boats prefer 87 AKI with low ethanol content. Check the manual; some recommend ethanol-free fuel to avoid storage and rubber component issues.

Storage and octane loss

Gasoline can degrade over months. Use fresh fuel in seasonal equipment, add stabilizer for storage, and keep containers sealed. Degradation affects volatility and can contribute to drivability issues.

Octane boosters and additives

Retail “octane boosters” often raise octane by only fractions of a point per bottle. They’re not a substitute for using the manufacturer-specified grade.

Gasoline vs. diesel

Diesel engines use cetane ratings, the opposite concept: cetane measures ease of ignition in compression-ignition engines. Never mix the fuels.

Summary

Octane measures a gasoline’s resistance to knock, not its power or quality. Use the grade your vehicle specifies: regular (87 AKI) suits most engines; premium (91/93 AKI) is for high-compression or boosted engines that require or recommend it. Higher octane won’t clean your engine or guarantee better mileage, but it’s essential for engines designed to exploit it, especially under heavy load or high heat.

Why is 93 octane better than 87?

93 octane is not inherently “better” than 87 octane; it is only beneficial for high-compression engines found in high-performance vehicles, where its higher resistance to detonation prevents engine knock and allows the engine to perform at its peak potential. For standard cars, trucks, and SUVs, 87-octane fuel is optimized for performance and efficiency, and using higher-octane fuel is unnecessary and an expense. 
What is Octane?

• A measure of resistance to knock: Octane ratings indicate how well fuel can withstand compression before it prematurely ignites, a phenomenon called detonation or engine knock. 
• Higher octane, higher compression: 93-octane fuel is more stable and can withstand more compression than 87-octane fuel. 

When 93 Octane is “Better”

• High-compression engines: Performance and luxury vehicles often have high-compression engines, which are designed for higher pressure in the cylinders before combustion. 
• Prevents engine knock: High-octane fuel prevents this premature ignition in high-compression engines, which can cause knocking, loss of power, and potential engine damage. 
• Optimizes performance: By preventing knock, 93-octane fuel allows these engines to operate at their full potential for optimal performance and efficiency. 

When 87 Octane is Sufficient 

• Standard engines: Most standard cars, trucks, and SUVs are designed to run efficiently on 87-octane fuel. 
• No additional benefits: Using higher-octane fuel in these vehicles provides no added benefits and can be a wasteful expense. 
• Slower burn rate: Some engines optimized for lower octane fuel may even perform worse with higher-octane fuel due to its slower burn rate. 

In Summary

• Check your owner’s manual: Always refer to your vehicle’s manufacturer’s recommendations for the correct octane rating. 
• Don’t overpay for premium: If your car doesn’t require premium fuel, stick with 87-octane for optimal performance and to avoid unnecessary costs. 

Does higher octane gas make a difference?

Higher octane gas makes a difference if your engine is designed for it, as it prevents engine knocking in high-compression or turbocharged engines by resisting detonation. Using higher octane fuel in a vehicle that doesn’t require it offers no benefit, as the fuel’s purpose is to withstand more heat and pressure, not provide extra energy or cleaning. Always check your vehicle’s owner’s manual or the sticker near the fuel filler cap to see if a higher octane is recommended or required. 
How Octane Works

• Resistance to Knock: Octane measures a fuel’s ability to resist “knocking” or pre-ignition. Knocking occurs when the air-fuel mixture in the engine combusts prematurely due to heat and pressure before the spark plug ignites it. 
• Slower Combustion: Higher octane fuel burns more slowly and evenly, reducing the risk of knocking. 

When Higher Octane Gas Makes a Difference 

• Engine Design: Vehicles with high-compression or turbocharged engines are designed to benefit from higher octane fuel. The higher compression requires a more knock-resistant fuel to prevent detonation.
• Increased Performance: For cars designed for higher octane, it can improve engine efficiency, power, and reduce emissions.

When Higher Octane Gas Makes No Difference 

• Regular Engines: Opens in new tabIf your car is designed to run on regular 87-octane gas, using a higher octane fuel provides no performance or efficiency benefits.
• No Extra Energy: Opens in new tabOctane ratings are not an indicator of energy content. The fuel doesn’t have more “energy” just because it has a higher octane rating.

Key Takeaway

• Check Your Manual: The best way to determine if higher octane gas makes a difference for your specific vehicle is to check your owner’s manual or the fuel filler cap for the recommended octane rating. 
• Follow the Recommendation: For standard engines, stick to the recommended octane level to avoid wasting money on fuel that won’t provide any benefits. 

Which is better, 91 or 95 octane?

Both 91-octane and 95-octane fuels have advantages. While 91-octane fuel is cost-effective and widely used, 95-octane fuel provides better engine performance. Protecting your vehicle with car insurance is equally important, regardless of your choice.

Is octane the same as regular gas?

Regular gas has the lowest octane rating, Premium has a higher octane and Super (or Supreme or Premium Plus) has the highest octane. Octane is the measure of the fuel’s ability to resist “knock”. Knocking or pinging are the loud noises that occur when the air/fuel mixture is incorrect.