Regular, midgrade, premium and super gasoline: octane grades explained
If you are weighing premium vs super gas, the short answer is that "super" is usually not a separate fuel. At most US stations it is a brand or marketing name for the top grade, which is premium. The number that matters is the octane rating printed on the pump, not the name on the button. Which grade your car needs depends on what the vehicle manufacturer specifies for your engine, not on the label a fuel retailer chooses.
The direct answer: what the grade names mean
US gas stations typically sell three grades of gasoline. The names vary by brand, but the structure is consistent: a lowest-octane grade, a middle grade and a highest-octane grade. Some stations use words like "super," "super premium," "ultra" or "plus" instead of regular, midgrade and premium. Because these names are not standardized, the only reliable way to compare fuels is the octane number displayed on the pump.
Common grade name | Typical US pump octane | Other names you may see; Regular | 87 (85 in some high-altitude areas) | Unleaded, regular unleaded; Midgrade | 89 (sometimes 88 or 90) | Plus, special, mid grade; Premium | 91 to 93 (varies by region and station) | Super, super premium, supreme, ultra
Treat these as typical ranges rather than guarantees. The exact octane for premium fuel differs between regions and retailers, which is why one station's premium may be 91 while another's is 93. If a station sells something labeled "super" alongside a separate "premium," check the posted number to see which is higher.
What an octane rating actually measures
An octane rating describes a fuel's resistance to knock, also called detonation or pinging. Knock happens when part of the air-fuel mixture ignites on its own from heat and pressure before the flame from the spark plug reaches it. That uncontrolled combustion creates pressure spikes that can reduce efficiency and, if severe and sustained, damage engine parts.
Higher octane does not mean more energy in the fuel, and it does not make gasoline "stronger" or cleaner by itself. It simply means the fuel tolerates more compression and heat before igniting on its own. Engines with high compression ratios, turbochargers or superchargers create conditions where that extra resistance can matter.
In the US, the number on the pump is the Anti-Knock Index, often shown as (R+M)/2. It is the average of two laboratory test results: the Research Octane Number (RON) and the Motor Octane Number (MON). Many other countries post RON alone, which produces higher-looking numbers. This is why a European or Australian fuel described as 95 or 98 is not directly comparable to a US 91 or 93 without accounting for the different method.
Premium gas versus unleaded: a common source of confusion
People often ask whether to choose premium or unleaded gas, but the comparison is a little misleading. All gasoline sold for road vehicles in the US is unleaded, including premium. At the pump, "unleaded" is commonly used as shorthand for the regular 87-octane grade. So premium gas versus unleaded really means premium versus regular: both are unleaded, and the difference is octane rating.
Midgrade gas octane and where it fits
Midgrade usually sits around 89 octane, between regular and premium. At many stations it is produced by blending regular and premium at the pump rather than being delivered as a separate fuel. Relatively few vehicles specifically call for midgrade. It can make sense when a manufacturer lists 89 as the recommended grade, or for an older engine that knocks on regular but does not need premium. Otherwise, most drivers will be better served by either the grade their manual requires or the lowest grade it allows.
How to know which grade your vehicle needs
The manufacturer's fuel specification is the deciding factor. It is usually stated in the owner's manual and often on a label inside the fuel filler door. Pay attention to the exact wording, because it changes the answer:
Regular (87) recommended: premium offers no meaningful benefit for an engine designed and tuned for regular fuel. Premium recommended: the engine can run on regular, but the computer may reduce ignition timing to prevent knock, which can lower power and fuel economy somewhat. Premium required: use the specified minimum octane. Running lower octane risks knock, reduced performance and possible engine damage, and may raise warranty questions. Minimum octane stated as a number: match or exceed that number on the pump, regardless of what the grade is called.
Fuel requirements can differ within the same model line depending on model year, engine, turbocharging and market. A base engine may take regular while a turbocharged or high-performance version of the same car requires premium. Always check the specification for your exact powertrain rather than relying on what applies to a similar vehicle.
What happens if you use a different grade
Using higher octane than required is generally harmless but usually wasteful. In an engine tuned for regular, premium will not add power, improve mileage or clean the engine in any noticeable way beyond what the detergents in quality gasoline already provide. Any difference you notice is likely to be small or due to other factors.
Using lower octane than specified is the riskier direction. Modern engines have knock sensors that detect early detonation and retard ignition timing to protect the engine, so an occasional tank of lower-octane fuel in a premium-recommended car is not usually an emergency. In a premium-required engine, however, repeated use of low-octane fuel, especially under heavy load, towing or high temperatures, can lead to persistent knock. If you hear pinging or rattling under acceleration, switch back to the specified grade.
Ethanol blends, altitude and fuel labeling
Most US gasoline is an ethanol blend containing up to 10 percent ethanol, commonly called E10. Ethanol raises octane, which is one reason it is widely blended into gasoline. Pumps typically carry a notice about ethanol content. Higher blends such as E15 and E85 are sold separately and are not suitable for every vehicle; fuel system compatibility and manufacturer approval for those blends are stated in the owner's manual or on the fuel door label.
In some high-altitude areas, particularly in parts of the Mountain West, the lowest grade may be posted as 85 octane. Thinner air reduces knock tendency in older carbureted engines, which is the historical reason for this practice. Modern fuel-injected engines adjust for altitude, and many manufacturers advise against using fuel below 87 octane. If your manual specifies a minimum of 87, follow it even where 85 is sold.
US fuel labeling rules require pumps to display the octane rating, usually on a yellow label. That posted number, not the grade name, is what tells you whether a fuel meets your vehicle's requirement. If a pump is labeled "super" or "plus" with no number you can find, choose a pump where the rating is clearly shown.
Choosing the right grade: a quick decision path
Find your vehicle's fuel specification in the owner's manual or on the fuel filler door. If it says regular or 87 octane, buy regular; higher grades are not necessary. If it says premium recommended, use premium for best performance, but regular is acceptable when needed. If it says premium required or lists a minimum of 91 or higher, buy fuel that meets that number. Ignore grade names such as super, plus or ultra, and compare the posted octane rating. Check ethanol labeling if your vehicle has restrictions on blends above E10.
In short, premium and super are typically the same top grade under different names, midgrade sits around 89 octane, and regular unleaded is the 87-octane baseline. The best choice is the lowest octane your manufacturer allows for your specific engine, and never lower than what it requires.
