General information only, last reviewed October 25, 2026. Full notice at the end of the page. A date on this page has passed. Check the current rule at the source before you rely on it. Dates to watch
Those yellow numbers on the pump, 87, 89, 93, are octane ratings. Drivers ask about them at the counter, and the grades behave differently in your tanks and on your margin. This page covers what octane measures and what the grade split means for a station's numbers.
What octane measures
Octane measures a gasoline's resistance to knocking, the premature, uncontrolled combustion that can damage an engine. Higher octane means more resistance to knock. The pump number is the rating that tells a driver how knock-resistant a grade is.
87, 89, 93
In the US the posted number is usually the anti-knock index, an average of two test methods. Regular is commonly 87, midgrade around 89, and premium typically 91 to 93. Higher numbers mean higher octane, which some engines require and others do not need.
Higher is not always better
Premium is what some engines, often higher-performance or turbocharged, require to run properly. For an engine built for regular, premium generally adds no meaningful benefit. Octane matches the fuel to the engine. An 87-octane engine gets nothing extra from 93, which is worth remembering when a customer asks.
How midgrade is made
Most stations carry two gasoline tanks, regular and premium. The dispenser blends midgrade on the fly, usually a 50/50 mix that lands at 89 octane. EIA prime supplier data shows how complete this shift is: midgrade is only about 1 percent of upstream gasoline volume, because almost nobody delivers finished 89 anymore. The 89 button sells fuel that arrived at the station as two other grades.
The grade mix in numbers
The mix is moving toward the high end. Department of Energy figures show premium growing from 8 percent of refiner gasoline sales in 2008 to about 13 percent by 2021, pushed by turbocharged engines that call for it. The retail spread is wide: AAA national averages in late 2025 put regular near $3.02 and premium near $3.98, roughly 96 cents apart, and Energy Department data shows that gap widening steadily since 2011. Spreads drift, so confirm current figures, but the direction has held for over a decade. Setting your own spread sits alongside how you price fuel overall and what each grade contributes to margin.
A blended-midgrade reconciliation example
Say a store sells 100,000 gallons in a month: 87,000 regular, 4,000 midgrade, and 9,000 premium. With a 50/50 dispenser blend, those 4,000 midgrade gallons drew about 2,000 from each tank. What the tanks gave up looks like this:
- Regular tank: 89,000 gallons (87,000 sold as regular plus 2,000 blended into midgrade)
- Premium tank: 11,000 gallons (9,000 sold as premium plus 2,000 blended into midgrade)
- Midgrade tank: zero, because there is no midgrade tank
Book those 4,000 gallons against a midgrade product with its own tank and your variance report will never tie out. The back office has to allocate blended sales to the source tanks before grade margins or tank reconciliation mean anything. FastDragon C-store does that allocation automatically, so each grade's volume and margin reconcile to the tanks that fed it.
Questions we hear a lot
Is Unleaded 88 the same as midgrade 89?
No. Unleaded 88 is E15, gasoline with up to 15 percent ethanol, and the extra ethanol is what raises its octane to 88. Midgrade 89 is usually a dispenser blend of regular and premium with the standard 10 percent ethanol, and the two are labeled and regulated as separate products.
Why do some states sell 85 octane as regular?
High-altitude areas in the Rocky Mountain states have long sold 85 or 86 octane as regular because thinner air lowers cylinder pressure and reduces knock. Modern engines compensate for altitude on their own, so most manufacturers still call for 87 or higher even there. NIST Handbook 130, the model fuel rule NIST publishes for states, allows 85 to be called regular only in those high-altitude areas, and each state sets its own rule, so check state law before treating 85 as regular.
What happens if a car that requires premium gets regular?
Most modern engines detect knock and pull ignition timing back, so the car loses some power and fuel economy and avoids damage. Older engines without knock sensors can be harmed by sustained knocking. If the owner's manual says premium is "recommended," regular is generally safe.
Who regulates the octane number posted on the pump?
The FTC's Fuel Rating Rule requires the familiar yellow and black octane label, and the posted number must match the rating certified up the supply chain. State weights-and-measures agencies pull fuel samples and test dispensers for compliance. A mislabeled grade can bring fines at the station even when the error happened upstream.
Does premium gasoline clean an engine better than regular?
Detergent additives do the cleaning, and they are separate from octane. The TOP TIER standard, backed by major automakers, requires detergent levels above the EPA minimum in every grade a licensed brand sells. A non-TOP TIER premium only has to meet the EPA minimum.
Sources: the FTC Fuel Rating Rule (16 CFR part 306, octane rating, certification, and label); EPA rules at 40 CFR 1090.80 (E15 definition) and 1090.260 (minimum detergent); the NIST Handbook 130 (2026) fuels regulation (minimum octane by grade name, including high-altitude areas); and the TOP TIER program.