Costco Gas Grades Explained: 87 vs 91 vs 93, Premium, and Why There's No Mid-Grade

Costco pumps usually have just two gasoline nozzles, and the numbers on them are not the same everywhere. This post settles what octane Costco premium gas actually is, why some stations show 85 or 93, why there is no mid-grade, and how much the premium habit costs you, using prices from our own tracker.

Short answer: Costco says its regular is "typically 87 octane" and its premium "typically 91 octane". In practice premium is 91 in most of the West and can be 93 in parts of the East, and high-altitude states often sell 85 as regular. As of our September 29, 2026 reading, Costco premium cost a median $0.64/gal more than regular in the US and 23¢/L more in Canada. The only difference between the two grades is octane.

What grades of gas does Costco sell?

Costco sells two gasoline grades, regular and premium, both under the Kirkland Signature name, plus diesel at a minority of stations. A few Iowa and Nebraska Costcos also sell E15, labelled Unleaded 88; see does Costco gas have ethanol. Its US gasoline FAQ says "Regular fuel is typically 87 octane and Premium fuel is typically 91 octane", and that octane is the only difference between the two. Both grades carry the same detergent package; see whether Costco gas is Top Tier for what that means.

Our data backs up the two-grade setup. Every one of the 592 US stations we track (excluding Puerto Rico) posts a regular and a premium price, and none posts a mid-grade price. In Canada, 77 of 78 gas bars show only regular and premium; the one exception in our data is Rimouski, QC, which lists a mid-grade price.

For diesel locations, see does Costco sell diesel.

Is Costco premium gas 91 or 93 octane?

It depends on the state, and sometimes on the station. Costco's own wording is "typically 91", and that is what you will see across California, the Pacific Northwest and much of the Mountain West. In parts of the East and Midwest, the premium that reaches a Costco can be 93. Jalopnik found that in states like Florida and Virginia premium can be 91 or 93 "depending on the station", and noted that Alaska's top grade is 90.

The cleanest way to know is the yellow octane label. The FTC's Fuel Rating Rule requires every US retailer to post the octane rating on each face of each dispenser. If the label on the premium nozzle says 93, that is what you are getting.

Why is premium 91 in the West and 93 in the East?

There is no single federal rule behind it. It comes down to regional refining and fuel specifications:

• California requires its own cleaner-burning reformulated gasoline, which limits aromatics and olefins, two of the components refiners use to raise octane. Premium in California settled at 91 around 2001, and virtually all of it is 91 today.
• Mountain states start from a lower baseline because regular there is often 85 or 86 (see below), and premium is typically 91.
• The East and Midwest are supplied by refineries and pipelines that ship higher-octane premium blendstock, so 93 is common.

The EIA describes premium nationally as "generally 91–94", so both numbers are normal premium.

What octane is Costco regular gas at high altitude?

In Colorado, Utah, Wyoming, Montana and other high-elevation areas, "regular" is often 85 octane, sometimes 86, and Costco follows the local market. Drivers report Costco stations in Colorado and Utah selling 85 as regular and 91 as premium, which lines up with what is sold around them. We have not found a Costco page listing octane by warehouse, so read the pump label.

The US Department of Energy's fueleconomy.gov explains that 85 was originally allowed at altitude because thinner air lowered the octane needs of older, carbureted engines. It says this is not true for modern engines and advises using the octane in your owner's manual even where 85 is sold. Many automakers say the same in their manuals. If your manual says 87 minimum, 85 is a step below it. At a Costco with only 85 and 91, the only way to meet an 87 requirement is to buy premium or mix the two (see the mid-grade section).

This matters most for turbocharged engines, which force air in and so do not get the same altitude break.

Prices in these states: Colorado Costco gas, Utah Costco gas and Montana Costco gas.

What does the octane number mean? AKI vs RON

The number on North American pumps is the Anti-Knock Index (AKI), shown as (R+M)/2. It is the average of two lab tests: the Research Octane Number (RON, a gentle test) and the Motor Octane Number (MON, a harsher one). The FTC rule defines the US pump rating this way.

Canada uses the same method. The Canadian General Standards Board gasoline standards, which provinces such as British Columbia write into law, set grades by AKI: regular 87, mid-grade 89, premium 91 and super-premium 93, all minimums. So a Canadian "91" means the same thing as a US "91".

Europe, Australia and most of the world post RON instead, which reads roughly 4 to 5 points higher for the same fuel. New to Canada or the US? Our newcomer's guide to Costco petrol in Canada maps pump numbers to the grades you know.

This is handy if you drive a European car whose manual lists "95 RON": that is roughly 91 AKI, which Costco premium meets. The conversion is approximate because the gap between RON and MON varies by fuel.

What octane is Costco premium gas in Canada?

Costco Canada does not publish an octane number for its premium. Its Canadian gasoline pages talk about detergent levels (five times the CGSB requirement) and Top Tier status, not octane. Canadian drivers on enthusiast forums report 91 on the pump label at Costco gas bars, which matches the CGSB minimum for premium. Some other Canadian brands sell a 93 or 94 top grade; Costco's premium is not that.

A note for Alberta searchers: "Costco 91 st" usually means the South Edmonton warehouse on 91 Street NW, not the octane. Its gas bar showed regular at 156.9¢/L and premium at 179.9¢/L in our September 29, 2026 reading: South Edmonton Costco gas prices.

Why doesn't Costco have mid-grade gas?

Costco does not explain it publicly, but the reasons are easy to see. Mid-grade is a small slice of gas sales, and a two-grade setup keeps pumps simple, lines moving and prices low. That fits the high-volume model covered in why Costco gas is so cheap.

Most cars do not need it either. In AAA's 2016 survey, 70% of US drivers had a vehicle that called for regular, 16% one that required premium, and only about 10% needed mid-grade.

At many other stations, mid-grade is not a separate fuel anyway. The station stores regular and premium underground, and the dispenser blends the two on the fly to make 89.

Can you make your own mid-grade at Costco?

Roughly, yes. Octane blends close to linearly, so a tank that is about half regular and half premium lands near the middle:

• 87 + 91 in equal parts gives roughly 89
• 87 + 93 gives roughly 90
• 85 + 91 gives roughly 88

You cannot hit an exact number because you will not know how much fuel was left in the tank, and pumps stop at dollar or gallon amounts, not ratios. If your manual lists mid-grade as a minimum, this is a reasonable workaround. If it says premium is required, buy premium.

Do you actually need Costco premium gas?

Only if your owner's manual or fuel-door label says premium is required. If it says premium is recommended, the car will run on regular with a small drop in power. If it says regular, premium does nothing for you.

• Premium required. Use it. Fueleconomy.gov says the extra cost is "absolutely" worth it in this case, because running low octane can cause knock that damages the engine over time.
• Premium recommended. Modern engines have knock sensors that retard ignition timing when they detect knock, so regular is safe but you give up some power and fuel economy. Fueleconomy.gov notes that the cost increase is typically higher than the fuel savings.
• Regular. Premium is wasted money. AAA tested regular and premium in cars built for regular on a dynamometer and found no significant gain in horsepower, fuel economy or emissions. It estimated Americans wasted more than $2.1 billion in a year on premium they did not need, and summed it up: premium is "higher octane, not higher quality."

At Costco the detergent additives are the same in both grades, so you are not buying a cleaner fuel when you pick premium.

How much more is Costco premium gas? Our price data

As of our September 29, 2026 reading, the average Costco regular in the US was $4.64/gal and the average premium was $5.32/gal. At the same station, premium cost a median $0.64/gal more than regular, and the middle 80% of stations sat between $0.40 and $1.04.

In Canada, the average Costco regular was 173.0¢/L and premium 195.7¢/L, a median gap of 23¢/L, with most gas bars between 20¢ and 25¢/L.

Costco premium gas price gap by state

The gap varies a lot by state. We took each station's latest regular and premium price, subtracted one from the other, and took the median per state (US, excluding Puerto Rico).

The pattern is clear. The narrowest gaps are in the West, where premium is typically 91, and California is lowest at 40¢ despite having the most expensive regular. The widest gaps are in the Great Lakes states: Michigan, Illinois, Ohio, Indiana ($1.04) and Wisconsin ($1.02). In Michigan and Illinois, premium costs about 25% more than regular. Part of that may be that premium in those markets is more often 93, but we do not have octane data per station, so treat that as a likely factor rather than a finding. Alaska ($0.45), Hawaii and Idaho (both $0.50) are also at the narrow end.

To check a single station, open its page from the US station list or Canadian list; each shows today's price by grade and 30 days of history.

What does premium cost a typical driver per year?

Take a US driver who covers 12,000 miles a year in a car that gets 25 mpg. That is 480 gallons.

For a Canadian driver covering 15,000 km at 9 L/100 km (1,350 L a year), the 23¢/L median gap works out to about $310 a year.

If your car requires premium, that is a cost of ownership. If it does not, it is money spent for no measurable benefit.

Frequently asked questions

What octane is Costco regular gas?

Costco says its regular is typically 87 octane, and that is what most US and Canadian stations sell. In high-altitude states such as Colorado and Utah, regular at Costco is often 85 or 86, so check the pump label.

Does Costco have 91 gas?

Yes. Premium at most US Costco stations is 91 octane, and in some eastern states it is 93 instead. In Canada, Costco does not publish its premium octane, but drivers report 91 at the pump, the CGSB minimum for premium.

Is Costco premium gas better than regular?

Only in octane. Costco says octane is the only difference between its regular and premium, and both carry the same detergent additives. Premium helps only in engines that require or recommend it.

Can I put Costco regular in a car that recommends premium?

Usually yes, if the manual says "recommended" rather than "required". The knock sensor will adjust timing to protect the engine, at the cost of a little power and fuel economy. If the manual says premium is required, use premium.

Is 85 octane at Costco safe for my car?

Fueleconomy.gov says 85 octane was allowed at altitude for older carbureted engines and that modern cars should use the octane in the owner's manual. If your manual says 87, 85 is below that; buy premium or mix regular and premium instead.

What is the Costco 91 gas price in Canada?

Costco premium (reported as 91 octane) averaged 195.7¢/L across the Canadian gas bars we track as of September 29, 2026, about 23¢/L above regular. Prices vary by province, from Alberta at the low end to Newfoundland and Labrador at the high end.

Is mixing Costco regular and premium bad for my engine?

No. Mixing grades of gasoline is safe, and many stations make mid-grade exactly this way. An even split of 87 and 91 gives roughly 89 octane.

Sources

• Gasoline Question and Answer, Costco — "Regular fuel is typically 87 octane and Premium fuel is typically 91 octane"; octane is the only difference between grades; use the octane in your owner's manual.
• Costco Gasoline, Costco Canada — Canadian page covers detergent (5X the CGSB requirement) and Top Tier, with no octane figures.
• Is Costco Premium Gas 91 Or 93 Octane?, Jalopnik — premium 91 or 93 depending on station in states like Florida and Virginia; Alaska tops out at 90; California premium is 91.
• 16 CFR Part 306, Automotive Fuel Ratings, Certification and Posting, eCFR — FTC definition of octane rating as (R+M)/2 and the requirement to label every dispenser face.
• Gasoline explained: octane in depth, U.S. Energy Information Administration — RON and MON definitions; regular generally 87, midgrade 89–90, premium 91–94.
• Growing octane needs widen the price difference between premium and regular gasoline, EIA — premium 91 to 93; why the premium price spread has grown.
• Selecting the right octane fuel, fueleconomy.gov (US DOE/EPA) — 85 octane at altitude, required vs recommended premium, knock sensors, premium and fuel economy.
• U.S. Drivers Waste $2.1 Billion Annually on Premium Gasoline, AAA Newsroom — 2016 dynamometer study; 70% of drivers need regular, 16% premium; "higher octane, not higher quality."
• Octane rating, Wikipedia — AKI used in the US and Canada vs RON elsewhere; AKI runs 4 to 6 points below RON for the same fuel.
• Cleaner Gasoline Regulation, B.C. Reg. 498/95, BC Laws — Canadian grade minimums by antiknock index: 87, 89, 91 and 93.
• Colorado is one of a few states that offers 85-octane gas, FOX31 Denver — 85 octane sold in Colorado, Wyoming and Utah above about 3,500 feet.
• Colorado Subaru owners: Costco gas octane, Subaru Outback Forums — driver reports of 85-octane regular at Colorado Costco stations (forum reports, not official).
• Costco Gas, Canadian Corvette Forums — driver reports of 91-octane premium at Canadian Costco gas bars (forum reports, not official).
• Your gas station has three fuel grades. So why does it only have two fuel lines?, Motor1 — mid-grade commonly blended in the dispenser from regular and premium.