Yes. Both “Costco Wholesale” and “Kirkland Signature” are licensed TOP TIER gasoline brands — you can read them off the program’s own brand list, where they appear for the United States, Canada, Mexico, Puerto Rico and Japan. The certification covers every octane grade at every one of those stations, because the standard does not let a marketer certify only its premium.
That is the whole answer to the question as most people ask it. It is also the point where two details start to matter: the licence stops at the border of the markets where the program operates, and diesel is certified station by station rather than brand-wide.
What Top Tier actually certifies
Top Tier is not a Costco badge, not an EPA program, and not a marketing tier invented by refiners. It is a fuel performance standard written by carmakers and administered on their behalf by the Center for Quality Assurance in Midland, Michigan. Twelve manufacturers sponsor it today: Audi, BMW, Daimler Truck, Ford, GM, Honda, International, Mercedes-Benz, Stellantis, Subaru of America, Toyota and VW.
It exists because of a quirk of regulation. The EPA set a minimum detergent level for all US gasoline in the mid-1990s, and the floor promptly became a target — several marketers cut their additive doses down to meet it and no more. Automakers wanted a level they could recommend in an owner’s manual without endorsing a brand, so in April 2004 they published the first Top Tier deposit control standard. A diesel version followed in October 2017.
What a licensed brand has to prove is unusually specific. These thresholds come straight out of the published performance standard, and they are a good deal less vague than “contains cleaning agents” on a pump sticker.
| Test | What has to happen |
|---|---|
| Intake valve deposits | The test fuel has to be dirty enough to leave at least 500 mg of deposits on its own. Dosed with the additive, the average must come in at 50 mg or less. |
| Combustion chamber deposits | Cleaning the valves must not dirty the chamber — deposits cannot exceed 140% of what the untreated fuel leaves behind. |
| Valve sticking | Cold soaks at −20 °C with the additive at three times its normal dose. A single stuck valve fails the test. |
| GDI injector cleanliness | Added in 2025: a 120-hour dyno run that fouls direct injectors for 60 hours, then requires the additive to claw back at least half the lost fuel trim and injector pulse width. |
| No-harm checks | Soot must not rise and pre-ignition events must be statistically no worse than on the base fuel. No manganese (MMT), ferrocene or other organometallic additives anywhere in that brand’s gasoline. |
The testing is done at an independent ISO 17025 laboratory that is barred from being affiliated with the fuel marketer or the additive maker. That independence is the program’s strength — and it also marks its limit. What gets approved is an additive package, together with the marketer’s licensed commitment to dose every grade at the approved rate. The program’s own FAQs for fuel marketers describe a voluntary licence carrying an annual fee scaled to station count, with no routine sampling of the fuel sitting in the tanks under your local warehouse. Certified means the chemistry and the commitment were verified. It does not mean your particular tankful was.
Where the certification applies — and where it cannot
Costco sells fuel in six countries and Top Tier operates in three of them. The program covers North America, a group of Central and South American countries, and Japan. There are no licensed brands at all in Britain, Australia or New Zealand — not Costco, not BP, not anyone.
| Country | Fuel stations | Gasoline | Diesel |
|---|---|---|---|
| United States | 570 | Listed — every grade | Listed, select sites (63 priced today) |
| Canada | 78 | Listed — every grade | Listed, select sites (6 priced today) |
| Mexico | 19 | Listed — Magna and Premium | No diesel sold |
| United Kingdom | 21 | Program not offered | Program not offered |
| Australia | 14 | Program not offered | Program not offered |
| New Zealand | 1 | Program not offered | Program not offered |
Puerto Rico is listed as its own market on the brand list, which is what covers the Costco fuel station we track there — priced by the litre rather than the gallon, but under the same Kirkland Signature licence. Japan is the newest entry: Costco became the first fuel marketer to sell Top Tier approved gasoline in Japan on 1 March 2024, starting with 22 stations.
Where the answer is no, that is a fact about the program’s footprint rather than a verdict on the fuel. British petrol must meet BS EN 228 and diesel BS EN 590 whoever sells it, and Costco still blends its own additive package into what it buys: its UK forecourts sell Kirkland Signature Unleaded, Premium Unleaded 97 and Premium Diesel. Australian and New Zealand sites are the same story — additised fuel meeting national fuel quality standards, with no North American certification mark available to put on the canopy.
Diesel is a separate licence, and a partial one
The gasoline rules are all-or-nothing: a marketer cannot pick which octane grades to certify. Diesel is deliberately looser — brands may enrol individual stations, and the diesel brand list shows Costco Wholesale and Kirkland Signature for the US and Canada with the qualifier “select locations only.” At an enrolled site, though, every grade of diesel under the canopy has to comply.
That maps onto how Costco sells diesel in the first place. In today’s feed, 63 of the 570 US stations and 6 of the 78 Canadian ones posted a diesel price — the pool an enrolled site can come from, which is why the pump decal is the thing to look for rather than the canopy. We keep the full station-level breakdown in our guide to which Costco locations sell diesel. In Mexico the question does not arise: the gasolineras sell Magna and Premium only.