The short answer
Yes.Costco's Kirkland Signature™ gasoline is officially Top Tier— both "Costco Wholesale" and "Kirkland Signature Gasoline" appear on the automakers' licensed-brands list, and the license covers every grade, so regular and premium alike qualify. Costco actually goes past the bar, blending about 5× the EPA's minimum detergent. The detail people love: the other big warehouse club, Sam's Club, is not on the Top Tier list.
"Top Tier" gets thrown around a lot at the pump, and it isn't just marketing — it's a specific, automaker-backed license a fuel has to earn. So when people ask "is Costco gas Top Tier?"they're really asking two things: is the claim genuine, and does it make any difference to my engine? Here's the proof Costco qualifies, what the standard actually demands, and the independent test that shows it matters.
Yes — Costco is on the official Top Tier list
Top Tier isn't something a station can simply claim; it's a license, and the authority that grants it publishes exactly who holds it. On the official Top Tier licensed-brands list, Costco shows up twice — as Costco Wholesale and as Kirkland Signature Gasoline — across the U.S., Canada, Puerto Rico, Mexico, and Japan.
Two things follow from being on that list. First, the certification is real and independently verifiable — you don't have to take Costco's word for it. Second, the Top Tier license applies to every octane gradea licensed retailer sells, so it isn't just the premium that qualifies — Costco's 87-octane regular is Top Tier too. Costco's Kirkland Signature fuel has carried the license since 2014.
What "Top Tier" actually means
Back in 1996 the EPA set a minimum detergent-additive requirement for all U.S. gasoline, to limit the gunk that builds up on intake valves and injectors. Automakers watched the next several years and decided the floor was too low — engines were still coking up. So in 2004, four of them — BMW, General Motors, Honda, and Toyota — created the Top Tier Detergent Gasoline standard to demand more. The group has since grown to include Ford, Stellantis, Volkswagen, Audi, Mercedes-Benz, and others.
To license the Top Tier mark, a fuel has to clear two bars: carry roughly two to three times the EPA's minimum detergent additive, and drop the cheap metallic additivesthat can themselves leave deposits. It's a performance spec set by the companies that build the engines — which is why "Top Tier" carries weight that a vague "premium quality" sticker doesn't.
Costco doesn't just meet the bar — it clears it
Plenty of brands meet the Top Tier minimum. Costco says it goes further: its Kirkland Signature gasoline contains about five times the EPA's required detergent — in both regular and premium — and the additive package is independently registered with the EPA. Here's how the three tiers stack up:
| Standard | Detergent additive | Metallic additives |
|---|---|---|
| EPA minimum (the federal floor) | 1× — the baseline every U.S. gallon must meet | Allowed |
| Top Tier standard | Roughly 2–3× the EPA minimum | Banned |
| Costco Kirkland Signature™ | About 5× the EPA minimum | Banned (Top Tier licensed) |
Costco can pour that much detergent without raising the price because it controls the blend itself: it adds the additive on-site as tankers are delivered, rather than buying pre-mixed fuel. The base gasoline, by the way, comes from the same major refineries that supply the branded station down the street — the Top Tier detergent dose is the part that makes it "Kirkland Signature."
Does Top Tier actually do anything? What AAA found
This is where it stops being a logo. In 2016, AAA commissioned an independent lab to settle it: it ran engines through the equivalent of 4,000 miles on Top Tier and non-Top Tier fuels, then took them apart and weighed the carbon deposits.
The gap was enormous. Non-Top Tier fuels left 19 times more carbon deposits — about 660 mg of gunk per intake valve, versus roughly 34 mg on Top Tier fuel. Those deposits are exactly what cause rough idling, hesitation, and a slow slide in fuel economy, and AAA found that switching to a Top Tier fuel can scrub some of the existing buildup back off over a few thousand miles.
The kicker is the price. Across a year of tracking, AAA measured Top Tier gas at only about three cents a gallon more than ordinary gas on average. At Costco you usually get the cleaner fuel for less than the station next door, not more — so you're not paying a premium for the Top Tier detergent at all.
Costco vs. Sam's Club: the Top Tier line
The most-searched follow-up is the warehouse-club showdown — and this is the cleanest difference between them. Costco is Top Tier licensed; Sam's Club is not. Sam's Club simply doesn't appear on the licensed-brands list.
To be fair to Sam's: its fuel still meets every federal EPA standard, so it won't hurt your car, and many drivers use it for years without issue. The difference is the extra, automaker-backed detergent package that Top Tier requires and Costco exceeds. If Top Tier is the deciding factor for you, Costco is the warehouse club that has it.
| Costco | Sam's Club | |
|---|---|---|
| On the official Top Tier list? | Yes — every grade | No |
| Detergent level | ~5× the EPA minimum | Meets the EPA minimum |
| Meets federal (EPA) fuel standards? | Yes | Yes |
| Automaker-backed detergent package? | Yes | No |
What about premium and diesel?
Premium is covered. Because the license applies to every octane grade, Costco premium is just as Top Tier as the regular — and the two share the identical detergent dose. The only real difference between them is the octane rating (about 87 vs. 91), not the additive package.
Diesel has its own Top Tier standard, separate from the gasoline one, and Costco earns that too: its Kirkland Signature Diesel — sold at select warehouses — has been certified to the Top Tier Diesel performance standard since 2017, with extra detergents and added lubricity on top of the usual ultra-low-sulfur formula.
The bottom line
So, is Costco gas Top Tier? Yes — unambiguously. Costco is on the automakers' official licensed list in every gasoline grade, it pours about five times the EPA's minimum detergent, and the AAA evidence says that keeps engines markedly cleaner. You typically pay lessthan nearby stations for it, not more, and Sam's Club — the obvious alternative — doesn't carry the certification at all. The fuel-quality question is settled; from there it's really about price and convenience. You can see how today's Costco prices compare where you live on our live price pages.
Fuel certifications and additive formulas change over time — details were last reviewed in June 2026. The Top Tier licensed-brands list is the authoritative, up-to-date source for which retailers qualify. This site is independent and not affiliated with Costco Wholesale Corporation.
