Costco gas is cheap, and cheap makes people suspicious. If you have wondered whether Kirkland Signature gasoline is real Top Tier fuel, whether it is as good as Shell or Chevron, or whether saving 20 or 30 cents a gallon is doing quiet damage to your engine, this post settles it with the primary sources: the Top Tier licence list, Costco's own fuel pages, and the AAA engine study that made Top Tier famous.
Short answer: Yes, Costco gas is Top Tier. "Costco / Kirkland Signature" is on the official Top Tier licensed gasoline list for the USA and Canada (plus Puerto Rico, Mexico and Japan), and the licence covers every grade, including regular. Costco says Kirkland Signature gasoline carries five times the government's minimum detergent level in both regular and premium.
Is Costco gas Top Tier in 2026?
Yes. As of September 2026, the Top Tier program's licensed gasoline brands page lists "Costco / Kirkland Signature" as a separate entry for each of these markets:
| Market | Top Tier gasoline | Top Tier diesel |
|---|---|---|
| United States | Listed | Listed |
| Canada | Listed | Listed |
| Puerto Rico | Listed | Listed |
| Mexico | Listed | Listed |
| Japan | Listed | Listed |
Costco says the same thing on its own sites. The US Costco gasoline page states that "Costco is listed as a TOP TIER gasoline retailer." The Canadian Kirkland Signature gasoline page says Costco Canada has been listed as a Top Tier gasoline retailer since December 2014.
Top Tier status is a licence, not a one-time badge, so it can in principle change. If you want to check for yourself, the Top Tier station finder and the brand list are the authority, and both showed Costco when we checked on September 29, 2026.
Is regular Costco gas Top Tier, or only premium?
Every grade counts. The Top Tier site says approved stations offer Top Tier fuel "across all octanes with no added cost at the pump," and Consumer Reports notes the standard applies to all grades from regular to premium. Costco's own claim of five times the detergent minimum also names "both regular unleaded and premium grades."
That matters for your wallet. As of our September 29, 2026 reading, premium cost a median $0.64 a gallon more than regular at the same US Costco, and about 23¢/L more at Canadian gas bars. You do not pay that gap to get the cleaning additives. Buy premium only if your car requires it; our guide to Costco gas grades and octane explains when it does.
What is Top Tier detergent gasoline?
Top Tier is a voluntary fuel standard written by carmakers, not the government. It requires more deposit-control additive than the legal minimum and bans organometallic additives that can damage emissions equipment (Top Tier).
Why automakers created it
The US EPA set a minimum detergent level for all gasoline in the mid-1990s. According to the AAA 2016 study, some automakers felt that minimum was not enough to keep modern engines clean. In 2004, General Motors, with BMW, Toyota and Honda, wrote a higher-detergency gasoline specification, which became Top Tier (Top Tier history).
Since 2015 the program has been run by the Center for Quality Assurance as program administrator, which handles licensing and auditing. A diesel version followed in 2017 to 2018.
Which automakers back Top Tier
The Top Tier home page lists these sponsors in 2026:
- Audi, BMW, Ford, GM, Honda, Mercedes-Benz, Stellantis, Subaru of America, Toyota, Volkswagen
- Daimler Truck and International (for diesel)
Many of these brands recommend Top Tier fuel in their owner's manuals. None of them require a particular gas brand.
What the extra detergent does
Detergent additives keep carbon from building up on fuel injectors and intake valves. Heavy deposits can cause rough idling, hesitation on acceleration, knocking and worse fuel economy. The problem is sharper in direct-injection (GDI) engines, which are now common in ordinary cars, and Consumer Reports points to GDI as a reason the standard matters more today.
What did the AAA Top Tier study find?
In 2016 AAA had an independent, ISO 17025-certified lab run a standard ASTM engine test on Top Tier and non-Top Tier gasolines bought in a southern Texas market. After the equivalent of 4,000 miles, the non-Top Tier fuels left 19 times more engine deposits than the Top Tier brands (AAA).
| AAA 2016 finding | Result |
|---|---|
| Deposits, non-Top Tier vs Top Tier | 19 times more with non-Top Tier |
| Existing intake valve deposits after switching to Top Tier | Cut by 45 to 72% over 5,000 miles (as reported by Consumer Reports) |
| Price difference over 12 months | About 3 cents a gallon more for Top Tier |
| US drivers not regularly buying enhanced-detergent gas | 47% |
Two honest caveats. AAA did not publish results for Costco specifically, and the test is now ten years old. What it shows is that the gap between minimum-detergent gas and Top Tier gas is real and measurable, and Costco sits on the Top Tier side of that line.
What is in Kirkland Signature gasoline?
Kirkland Signature gasoline is ordinary base gasoline plus Costco's own detergent additive package. Costco does not publish the additive's chemical name or supplier, so any specific product name you see online comes from forums, not from Costco.
Here is what Costco does state:
| Claim | United States (costco.com) | Canada (costco.ca) |
|---|---|---|
| Top Tier listed | Yes | Yes, since December 2014 |
| Detergent level | Five times the EPA requirement | Five times the CGSB requirement |
| Grades covered | Regular unleaded and premium | Regular unleaded and premium |
| Testing | "Extensive engine tests at nationally-recognized laboratories" | Testing "shows that Kirkland Signature Gasoline cleans up dirty engines and keeps them clean" |
Costco's auto program article on why gasolines are not created equal adds more detail. Costco commissioned intake valve deposit testing from accredited labs, concluded the optimum dose was "approximately five times the government minimum," and says consistent use removed the majority of intake valve deposits. It also says Kirkland Signature gasoline "meets and exceeds" the Top Tier standard.
Keep in mind these test results come from Costco, not from an independent published study. The independent check is the Top Tier licence itself, which requires additives with accredited performance testing and ongoing audits.
Where does Costco gas come from?
Costco does not own refineries. It buys finished gasoline from the same regional refiners, pipelines and terminals that supply other stations in each area, and adds its own detergent. Our post on where Costco gets its gas covers the supply chain and what is known about Costco's suppliers.
The US Energy Information Administration explains that fuel from different refiners is mixed, or "commingled," in shared pipelines, and that competing companies often buy from the same terminal. EIA says the only real difference between brands is "the small amount of additives they might blend into gasoline before delivery" (EIA). Base gasoline at a given terminal has to meet the same fuel specifications whoever buys it.
Where Costco differs is how it adds the detergent. Most brands have their additive injected at the terminal. Costco's auto program article says it chose to "blend the additives at Costco gas stations during the fuel delivery," using an on-site system it designed so it controls the process and the dose. Practices can vary by region and over time, but that is what Costco has published.
So the gas in a Costco tank may well come from the same refinery as the branded station across the road. What makes it Kirkland Signature is the additive package and the price.
Is Costco gas as good as Shell, Chevron or Exxon?
For keeping a normal engine clean, yes. Shell, Chevron, Exxon and Mobil are all on the same Top Tier list as Costco, so all of them meet the same automaker-written detergency floor, in every grade.
Above that floor, brands differ. Shell, Chevron and Exxon market their own additive formulas, and AAA noted that results varied between brands because detergent packages differ. No independent public test we found ranks Costco against Shell or Chevron head to head, so anyone claiming one is clearly "better" is going beyond the evidence. Costco's five-times-the-minimum claim is a strong dose on paper, but it is Costco's figure.
The practical point: both a branded Top Tier station and Costco clear the bar that automakers set. The difference you can measure is price. As of our September 29, 2026 reading, the average Costco regular was $4.64 a gallon across 592 US stations and 173.0¢/L across 78 Canadian gas bars. For why Costco undercuts nearby stations, see why Costco gas is so cheap.
Does Costco gas have ethanol?
Yes, usually up to 10% (our Costco ethanol guide covers E10, E15 and ethanol-free fuel). Costco's fuel pages do not list an ethanol figure, but pump labels show it, and the EIA says most gasoline sold in the US is E10, about 10% ethanol by volume. Costco gas is no different from other stations on this.
In Canada, federal and provincial rules require renewable content in gasoline, and the levels differ by province (Government of Canada, Clean Fuel Regulations). Ethanol blends are the norm at Canadian gas bars too. If you need ethanol-free fuel for a boat, small engine or classic car, Costco is generally not the place; check the pump label at your warehouse.
Is Costco gas bad for your car?
No. The common worries do not hold up (our Costco gas myths post takes each one in turn, with real contamination incidents):
- "It's cheap, so it must be low quality." Costco's low price comes from its membership model and high volume, not a lower fuel spec. The base gas meets the same standards as everyone else's.
- "It's watered down or off-spec." Base fuel is tested through the pipeline and terminal system before delivery, and Costco's gas carries more detergent than the legal minimum, not less.
- "It will void my warranty." Automakers ask you to use gasoline of the right octane and ethanol content. Several recommend Top Tier, which Costco is.
Bad fuel incidents (water in a tank, a contaminated delivery) can happen at any station, branded or not. They are not a Costco-specific problem.
What about Kirkland Signature diesel?
Where Costco sells diesel, it is also Top Tier. "Costco / Kirkland Signature" appears on the Top Tier diesel brands list for the US and Canada. Top Tier diesel approval is site specific, so look for the decal at the pump. Costco says its diesel includes additives for injector cleanliness, cold starting and wear protection. Only some warehouses sell diesel (67 US stations and 6 Canadian ones report a diesel price in our data), and our post on which Costco locations sell diesel covers where.
Should you fill up at Costco? The takeaway
If your car takes regular, Costco regular gives you Top Tier detergent at what is usually one of the lowest prices in town. You don't need premium for cleaning, you don't need a bottle of injector cleaner on top of Top Tier fuel for normal driving, and you are not trading engine health for savings.
Check today's price at the warehouse you use with our Costco gas price finder. State pages such as California, Texas and Washington, and province pages such as Ontario and British Columbia, include a Kirkland Signature fuel section alongside hours and grades. You can browse all US Costco gas stations or Canadian Costco gas bars.
Frequently asked questions
Is Costco a Top Tier gas station in Canada?
Yes. "Costco / Kirkland Signature" is listed separately for Canada on the Top Tier gasoline and diesel brand lists, and Costco.ca says Costco Canada has been a Top Tier gasoline retailer since December 2014. Its gasoline carries five times the Canadian (CGSB) detergent requirement, according to Costco.
Is Costco 87 octane gas Top Tier?
Yes. The Top Tier licence applies to every octane a licensed retailer sells, so Costco's regular is Top Tier just like its premium. Costco says both grades carry five times the EPA detergent minimum.
Is Costco gas good quality?
Yes. Costco sells Top Tier licensed gasoline made from the same base fuel other stations buy, with an added detergent package Costco says is five times the government minimum. Independent testing by AAA found Top Tier fuels leave far fewer engine deposits than minimum-detergent gas.
Who supplies Costco's gas?
Costco buys gasoline from regional refiners and fuel terminals, the same supply system used by branded and unbranded stations, and the supplier can differ by area. Costco then adds its own Kirkland Signature detergent additive, which it says is blended at the station during fuel delivery.
Do I need to add fuel injector cleaner if I use Costco gas?
For normal driving, generally no. Top Tier fuels are designed to prevent deposits and, according to AAA, can reduce existing intake valve deposits over a few thousand miles. Follow your owner's manual if it gives specific advice.
Is Top Tier gas worth it?
AAA's 2016 testing found non-Top Tier gas left 19 times more engine deposits, and Top Tier cost only about 3 cents a gallon more on average. At Costco there is no premium for Top Tier at all, since its regular is already Top Tier and usually priced below nearby stations.
Does Costco gas have more ethanol than other stations?
No. Costco gas is typically E10, up to 10% ethanol, which is the same as most gasoline sold in the US. The ethanol content is shown on the pump.
Sources
- Licensed gasoline brands, Top Tier — Costco / Kirkland Signature listed for USA, Canada, Puerto Rico, Mexico and Japan; standard applies to every grade.
- Licensed diesel brands, Top Tier — Costco / Kirkland Signature diesel listings by country; approval is site specific.
- Top Tier home page — current automaker sponsors; "every octane, no added cost."
- Top Tier history, Top Tier — 2004 origin with GM, BMW, Toyota and Honda; Center for Quality Assurance as administrator since 2015; diesel standard.
- Costco Gasoline (Fuel Promise), Costco.com — Top Tier listing, five times the EPA detergent requirement in regular and premium, engine testing, diesel additives.
- Kirkland Signature Gasoline, Costco.ca — Canadian Top Tier listing since December 2014, five times the CGSB requirement.
- Gasolines Are Not Created Equal, Costco Auto Program — on-site additive blending at delivery, intake valve deposit testing, five times the government minimum.
- AAA Study Indicates Not All Gasoline Is Created Equal, AAA Newsroom — 19 times more deposits, test method, 3-cent price gap, 47% of drivers.
- About TOP TIER, toptiergas.com — the ban on organometallic additives.
- Top Tier Gasoline Is Worth the Extra Price, Consumer Reports — all grades covered, 45 to 72% deposit reduction, GDI context, Costco on the list.
- Where our gasoline comes from, U.S. EIA — commingling in pipelines and terminals; brands differ mainly by additives.
- How much ethanol is in gasoline, U.S. EIA — most US gasoline is E10.
- What are the Clean Fuel Regulations, Government of Canada — Canadian renewable fuel rules context.