Are “Octane 91” and “Unleaded 91” the Same?

They can be the same, but it depends on where you are and which octane scale is being used. In countries that label fuel by RON (Research Octane Number), “Unleaded 91” and “91 octane” generally refer to the same regular petrol. In the United States and Canada, however, “91 octane” means a premium grade measured by AKI (Anti‑Knock Index), not the regular fuel; there, regular unleaded is typically 87 AKI.

What the Terms Mean

Octane rating scales explained

Octane ratings measure a fuel’s resistance to knock (pre‑ignition). The number on the pump can come from different test methods, so a “91” in one country isn’t always equal to a “91” elsewhere.

• RON (Research Octane Number): Common in Europe, Australia, New Zealand, much of Asia and the Middle East. Labels like 91, 95, 98 are RON.
• MON (Motor Octane Number): A tougher test yielding a lower number; used with RON to compute AKI.
• AKI (Anti‑Knock Index, a.k.a. (R+M)/2): Used in the U.S. and Canada. Typical posted grades are 87 (regular), 89 (midgrade), 91–93 (premium).
• Conversion rule of thumb: AKI is usually about 4–6 points lower than the equivalent RON. For example, 91 AKI ≈ 95–96 RON.

Because pump labels use different scales, matching the number only works if you know which standard is posted at the pump.

Fuel naming conventions by region

Fuel names on pump labels vary widely, which is a common source of confusion when comparing “Octane 91” and “Unleaded 91.”

• United States/Canada: Pumps display AKI. All road gasoline is unleaded. Regular is usually 87 AKI; premium is 91–93 AKI. The phrase “Unleaded 91” isn’t a standard product name.
• Europe: Pumps display RON. Regular is commonly 95 RON (E5/E10). 91 RON exists but is less common in many countries.
• Australia: Pumps display RON. Common grades are Unleaded 91 (91 RON), E10 (typically labeled 94 RON), Premium 95, and 98. “Unleaded 91” is the regular grade.
• New Zealand: Pumps display RON. Common grades are 91 (regular), 95, and sometimes 98. Some retailers may offer ethanol‑blended variants; labeling varies by brand.
• Asia/Middle East: Many markets label by RON (e.g., 91/95). In places like Thailand, “Gasohol 91” (E10) and “Benzine 91” (non‑ethanol) are both 91 RON.

Knowing the local labeling standard is key: the same number can describe different products across regions.

When Are They the Same?

They’re the same when both terms refer to 91 RON in RON‑label markets—“Unleaded 91,” “91 octane,” or simply “91” usually mean the same regular petrol. They’re not the same in AKI markets like the U.S. and Canada, where “91 octane” is a premium fuel and there is no standard product called “Unleaded 91.”

How to Choose the Right Fuel for Your Car

These steps help you match your vehicle’s requirement to what’s on the pump wherever you’re driving.

1. Check your owner’s manual or fuel door: It states the minimum required octane and whether it’s expressed as RON or AKI, plus any ethanol limits (e.g., up to E10 or E15).
2. Match the scale: Use at least the posted minimum on the pump for your region’s scale (RON in many countries; AKI in the U.S./Canada).
3. If only higher octane is available, it’s safe: Using higher than required octane won’t harm the engine, but it rarely improves performance or economy in engines not designed for it.
4. Avoid lower octane than required: It can cause knocking and reduced performance; modern engines may pull timing to protect themselves, which can hurt efficiency.
5. Mind ethanol content: Octane rating and ethanol percentage are separate. Some 91 RON fuels are E0 (no ethanol), others are E10; use what your vehicle approves.

Following the manual’s minimum and matching the local pump’s rating system eliminates most confusion and protects engine health.

Common Misconceptions

Because “unleaded” and “octane” describe different attributes, several myths persist around fuel choice and performance.

• “Unleaded” vs octane: Unleaded means no lead additives (now standard for road fuel worldwide). It doesn’t specify octane.
• Higher octane = more power: Only if the engine is designed or tuned for it (high compression/turbo). Otherwise, no meaningful benefit.
• Detergents: Additive packages vary by brand and “Top Tier” certification, not strictly by octane number.
• Ethanol and octane: Ethanol generally raises octane, but energy content per liter is slightly lower; real‑world economy may drop a bit with higher ethanol blends.
• “Premium” means the same everywhere: It doesn’t. Premium is 91–93 AKI in North America, often 95–98 RON elsewhere.

Separating octane rating, ethanol content, and detergent quality helps you pick the right fuel for your needs without overpaying.

Quick Regional Answer Examples

Here are practical, region‑specific interpretations of the question to clarify what you’ll see at the pump.

• Australia/New Zealand: “Octane 91” and “Unleaded 91” both mean 91 RON regular petrol. Some stations also sell E10 (often labeled separately); check your car’s ethanol compatibility.
• United States/Canada: “91 octane” is a premium AKI fuel. Regular unleaded is 87 AKI. The label “Unleaded 91” isn’t standard here.
• Europe: If you encounter 91, it means 91 RON, but many stations start at 95 RON for regular. “Octane 91” equals 91 RON.
• Asia/Middle East: Many pumps offer RON 91 and 95. “Octane 91” and “91” are typically the same as 91 RON; check whether it’s ethanol‑blended if that matters for your vehicle.

Use the local octane scale and your owner’s manual as your guide; wording on the canopy can be marketing, but the number and scale on the pump are what count.

Summary

“Octane 91” equals “Unleaded 91” only when both refer to 91 RON, as in Australia, New Zealand, and many RON‑label markets. In the U.S. and Canada, “91 octane” denotes premium fuel measured by AKI, not the regular grade. Always match the octane scale posted at the pump to your vehicle’s specified minimum and consider ethanol compatibility separately.

Is 91 octane the same as unleaded?

Yes, 91 octane fuel is unleaded and is often categorized as a premium fuel, though it’s the standard for some regions or vehicles. The “unleaded” designation refers to the absence of lead, while the “octane” rating measures the fuel’s resistance to premature detonation or knocking in an engine.
 
Key points about 91 octane fuel:

• It is unleaded: All common grades of gasoline sold in most countries today are unleaded, meaning they do not contain lead. 
• It’s a premium grade: A 91 octane rating typically falls into the mid-grade or premium category, depending on your location and the specific fuel grades offered at the pump. 
• Resists knocking: Higher octane fuels, like 91, are more stable and resist premature combustion, which can cause engine knock and damage. 
• Check your car’s requirements: The most important factor is to use the fuel octane recommended in your vehicle’s owner’s manual. Using a lower octane than recommended can cause engine problems, while higher octane is rarely needed unless your engine is designed for it. 

What octane is unleaded?

Unleaded is not a single octane rating; instead, “unleaded” describes the absence of lead in gasoline, which has several octane levels including regular (typically 87), mid-grade (usually 89), and premium (91 or higher). The octane rating measures a fuel’s resistance to pre-ignition or engine knock. Regular unleaded (87 octane) is suitable for most standard vehicles, while high-performance vehicles may require mid-grade or premium fuel.
 
What “Unleaded” Means

• It’s a feature, not a specific octane: Opens in new tab”Unleaded” refers to gasoline that does not contain lead additives, which were phased out of gasoline for environmental and health reasons. 
• All unleaded gas has an octane rating: Opens in new tabYou’ll find different grades of unleaded gasoline at the pump, with varying octane levels. 

Common Unleaded Octane Ratings

• Regular Unleaded: This is the most common grade and typically has an octane rating of 87. It’s designed for the majority of everyday vehicles. 
• Mid-Grade Unleaded: Usually has an octane rating of 89 or 90 and is for vehicles that require a bit more resistance to pre-ignition. 
• Premium Unleaded: Has a higher octane rating, often from 91 to 94, making it more resistant to engine knock. This fuel is for high-performance vehicles. 

How to Choose

• Check your owner’s manual: The safest and most effective way to determine the correct octane is to consult your vehicle’s owner’s manual, which will specify the recommended octane rating. 
• Don’t use higher than needed: Unless your car’s manufacturer specifically recommends it, using premium fuel in a car designed for regular 87 octane gas provides no benefit and is simply a waste of money. 

What is a substitute for unleaded 91?

Opal is a direct substitute for regular unleaded 91, delivering comparable performance. It can be used in cars, boats and other engines. It’s safe to mix with regular unleaded 91, or higher octane fuels, and can be stored in the same way.

What gas is the same as 91 octane?

Premium gas, or high-octane gas, has an octane rating of 91 to 94.