87, 89 and 93 Octane Gas: Choosing the Right Grade for Your Car
Yes, 93 octane is premium gas. At most US stations, 87 is regular, 89 is mid-grade (often labeled plus), and 91 to 93 is premium. The right grade for your car depends on what the manufacturer specifies, not on the number alone. A higher number means the fuel resists engine knock better. It does not mean the fuel contains more energy, cleans the engine better, or makes every car faster.
What the Number on the Pump Means
The large number on a US gas pump is the octane rating. Octane measures how well gasoline resists igniting too early under compression. When fuel ignites before the spark plug fires, or burns unevenly in the cylinder, it causes knock. Knock is also called detonation or pinging. It can sound like a metallic rattle under acceleration. Sustained, severe knock can damage pistons and other engine parts.
US pumps show the Anti-Knock Index (AKI). It is the average of two laboratory measurements, the Research Octane Number (RON) and the Motor Octane Number (MON). That is why pumps often show the formula (R+M)/2 near the number. Many other countries post RON figures, which are numerically higher for the same fuel. A European 95 RON fuel and a US 91 AKI fuel can be roughly comparable. Keep this in mind when reading a manual written for another market.
87, 89 and 93 Compared
Grade | Common pump name | Typical use; 87 | Regular unleaded | Most mainstream engines designed for regular fuel; 89 | Mid-grade, plus, or special | Engines that call for 89, or owners following a manual that allows a middle grade; 91–93 | Premium, super, or supreme | High-compression or turbocharged engines that require or recommend premium
Premium availability varies by region. Some areas top out at 91 and others offer 93. Both are sold as premium, so a car that calls for 91 can use 93. At high-altitude stations you may see 85 or 86 octane labeled as regular. Many modern fuel-injected cars are not intended to run on it, so check your owner's manual before choosing a grade below 87.
What Is 87 Gas?
87 is the standard regular unleaded grade. It is what most mainstream cars, crossovers, pickups and minivans with non-performance engines are designed to use. If your owner's manual or fuel door says 87 or regular, that is the correct fuel. Buying a higher grade will not help the engine.
What Is 89 Gas?
89 is the mid-grade option, often called unleaded plus. Many stations do not store it in its own tank. Instead, the pump blends regular and premium to produce it. Few vehicles strictly require 89. It mostly makes sense when the manufacturer specifies it, or as a compromise in a car where premium is recommended but not required.
What Is 93 Gas?
93 is the highest common premium grade in many US markets. Engines with high compression ratios, turbochargers or superchargers, or aggressive ignition timing are often designed for premium. These engines create more cylinder pressure and heat, so they need fuel that resists knock better.
Required vs. Recommended: The Distinction That Matters
The most important detail is the exact wording in your owner's manual or on the fuel door label. Manufacturers generally use one of three phrasings, and each one changes the answer.
Regular (87) specified: use 87. Higher grades add cost without a meaningful benefit for an engine designed around regular fuel. Premium recommended: the engine is tuned to perform best on premium, but it can run safely on lower octane. Its knock sensors retard ignition timing to prevent knock. Expect some loss of power and possibly fuel economy on regular. Normal driving is not expected to cause damage. Premium required: use premium. Lower octane may cause knock, warning lights or reduced performance. Repeated use may risk engine damage, and some manufacturers note that damage from using the wrong fuel may not be covered under warranty.
The rules can differ within one model line. A base engine may take regular while a turbocharged or performance version of the same car requires premium. Requirements can also change between model years or generations. Always go by the documentation for your exact vehicle rather than general advice about the model name.
Does Higher Octane Improve Performance or Mileage?
In an engine designed for regular, generally no. The extra knock resistance goes unused because the engine is not producing enough cylinder pressure to need it. Gasoline grades have broadly similar energy content. Octane is about controlling combustion, not adding power.
In an engine designed for premium, higher octane lets the engine computer use the ignition timing it was calibrated for. That is how these engines reach their rated output. Running regular in a premium-recommended car usually reduces performance under load. The size of that loss depends on the engine and driving conditions.
Common Myths About Gas Types
Premium cleans the engine better: deposit control comes from the detergent additive package, not the octane rating. Detergent standards, such as Top Tier, apply to all grades sold under those programs. A tank of premium is a treat for the engine: if the engine does not need the knock resistance, it gains nothing. Mixing grades is harmful: grades from the same pump are compatible. Filling a premium-recommended car with a mix simply produces an octane level in between. One accidental tank of the wrong grade ruins an engine: putting 87 in a premium-required car once is usually manageable. Drive gently, avoid heavy loads and hard acceleration, and refill with premium as soon as you can. Putting premium in a regular-fuel car causes no harm.
What Else Differs Between Gas Types
Beyond octane, the main differences at US pumps are ethanol content and additives. Most standard US gasoline contains up to 10 percent ethanol, labeled E10. E15 and E85 are separate products with their own compatibility rules. E85 is meant for flex-fuel vehicles only. Diesel is an entirely different fuel and must never go into a gasoline engine. Seasonal blends that change with the weather also exist, but they are handled by fuel suppliers and do not require any choice from the driver.
How to Choose the Right Grade
Check the fuel door label or the fuel section of the owner's manual for your specific model year and engine. If it says regular or 87, buy 87. If it says premium required, buy 91 or 93, whichever premium grade your station offers. If it says premium recommended, decide between full performance on premium and lower cost on regular. Both are acceptable. If you hear persistent knocking on the specified grade, have the vehicle inspected rather than just switching fuels.
In short, 93 is premium, 89 is mid-grade, and 87 is regular. The best choice is the lowest grade your manufacturer specifies for your engine. Moving up a grade only pays off when the engine is built to use the extra knock resistance.
