The short answer
Yes. Costco gasoline is standard E10 — up to 10% ethanol— in both regular and premium, exactly like nearly all gas sold in the U.S. It's not ethanol-free, and Costco doesn't sell E15 or a "pure gas" option. The ethanol is there because federal renewable-fuel law puts it in almost all American gasoline — so the blend in your Costco tank is the same one you'd get at any major-brand pump. What actually sets Costco apart isn't the ethanol; it's the extra Top Tier detergent and the usually-lower price.
When people ask "does Costco gas have ethanol?" they're usually after one of two things: reassurance that the fuel won't harm their engine, or a source of ethanol-freegas for a boat or small engine. Here's what's actually in Costco's tank, why it's there, and what it means for your car — and for the mower.
Yes — Costco gas is E10
Costco's Kirkland Signature™ gasoline contains up to 10% ethanol — the blend known as E10— in both the 87-octane regular and the 91-octane premium. That's not unusual: more than 95% of the gasoline sold in the United States is E10. You don't have to take anyone's word for it, either — federal rules require the ethanol content to be labeled right on the pump, so every Costco dispenser shows it.
One myth worth killing: you'll see claims online that Costco's premiumis ethanol-free. It isn't. Both grades are E10; assume up to 10% ethanol unless a pump is explicitly marked "ethanol-free," which Costco's pumps are not.
Why is there ethanol in it? (It's the law, not Costco)
The ethanol isn't Costco's choice — it's policy. Most ethanol blending into U.S. gasoline happens to meet the Renewable Fuel Standard and the 1990 Clean Air Act, the federal programs (administered by the EPA) that require renewable fuel in the nation's gasoline supply. Because Costco buys finished gasoline from the same refineries that supply other brands in your region, it gets the same E10 base fuel everyone else does. The ethanol is baked into the supply long before it reaches the warehouse.
So what's actually in Costco gas?
Strip a gallon of Costco regular down to its parts and you get three things — and only one of them is really "Costco":
| Component | What it does | How much |
|---|---|---|
| Base gasoline | The fuel itself — from the same major refineries that supply other brands | About 90% |
| Ethanol | A renewable, corn-based oxygenate that federal law requires in the supply | Up to 10% (E10) |
| Top Tier detergent | Costco’s additive package — keeps injectors and valves clean; this is the real differentiator | ~5× the EPA minimum (trace by volume) |
The base gasoline and the ethanol are essentially identical to what the branded station down the street sells. The difference is that third row: Costco blends in about five times the EPA's required detergent and skips the metallic additives that leave deposits — enough to earn the automaker-backed Top Tier certification. The only thing separating regular from premium is octane (87 vs. 91); both carry the same E10 and the same detergent dose.
Can you get ethanol-free gas at Costco?
No — and this is the question that sends most people searching. Costco doesn't sell ethanol-free "pure gas" (often labeled REC-90), nor does it sell E15/ "Unleaded 88." If you need ethanol-free fuel, you'll have to find a specialty station, marina, or pump finder for it.
Why would you want it? Ethanol attracts moisture and can degrade over months of storage, and it can be hard on the rubber and older fuel systems found in boats, lawn mowers, generators, chainsaws, and classic cars. For gear that sits between uses, ethanol-free gas (or a fuel stabilizer) genuinely helps. For a car you drive every week, it's a non-issue — which brings us to the engine question.
Does the ethanol hurt your car or your gas mileage?
For any modern vehicle — roughly model year 2001 and up — E10 is completely fine. Automakers design and warranty their engines around it, and Costco's Top Tier detergent actively helps keep the fuel system clean.
The one real trade-off is a small one: fuel economy. Ethanol holds about a third less energy per gallon than pure gasoline, so a gallon of E10 delivers roughly 97% of the energy of ethanol-free gas. In practice, the EIA puts the hit at about 3% fewer miles per gallonon E10 (AAA and the EPA peg it at 3–4%). On a car that gets 30 MPG, that's about 29 — a difference most drivers never notice, and one that has nothing to do with Costco specifically, since the E10 is industry-wide.
What about Costco diesel?
Ethanol is a gasoline additive, so it isn't in diesel at all. Costco diesel (sold at select warehouses) is standard ultra-low-sulfur diesel, which may contain a little biodiesel where state law requires it — but never ethanol.
A note for outside the U.S.
Ethanol isn't only an American thing. The UK made E10 its standard unleaded grade in 2021, and E10 is widely sold across Australia, so Costco's petrol in those markets carries ethanol too. The specifics (and the pump labels) vary by country, but the headline is the same: standard unleaded almost always means E10.
The bottom line
Costco gas has ethanol — standard E10, up to 10%, in both grades, just like virtually every pump in the country. It's not ethanol-free, and Costco doesn't offer a pure-gas option, so it's the wrong stop if you specifically need ethanol-free fuel. But for any modern car, E10 is exactly what the engine expects. The ethanol is the boring, identical part; what makes Costco fuel worth seeking out is the Top Tier detergent and the price — you can check today's rates on our live price pages.
Frequently asked questions
Does Costco gas have ethanol?
Yes. Costco gasoline is standard E10 — up to 10% ethanol — in both regular and premium, the same as nearly all gasoline sold in the United States. Every Costco pump is labeled with its ethanol content.
Does Costco premium gas have ethanol, or less of it than regular?
Costco premium is also E10 — up to 10% ethanol, the same as regular. The only difference between the two grades is the octane rating (about 87 for regular, 91 for premium); the ethanol content and the detergent package are identical. The idea that Costco premium is ethanol-free is a myth.
Is Costco gas E10 or E15?
E10. Costco does not sell E15 (sometimes branded “Unleaded 88”) or any higher ethanol blend. Its gasoline menu is just regular and premium, both E10, plus diesel at select warehouses.
Does Costco sell ethanol-free gas?
No. Costco does not offer ethanol-free “pure gas” (REC-90) at its warehouses. If you need ethanol-free fuel for a boat, small engine, generator, or classic car, you’ll have to find a specialty station or marina that sells it.
Does the ethanol in Costco gas lower MPG or hurt my engine?
It’s fine for any modern car (roughly 2001 and newer), which are all built to run on E10. Because ethanol carries about a third less energy per gallon than gasoline, E10 trims fuel economy by about 3% versus ethanol-free gas — on a 30-MPG car, roughly 29 MPG. Most drivers never notice.
Does Costco diesel have ethanol?
No. Ethanol is blended into gasoline, not diesel. Costco diesel is standard ultra-low-sulfur diesel (ULSD), with biodiesel content only where state law requires it.
Fuel blends and pump labeling are set by federal and state rules that change over time — figures were last reviewed in June 2026. Always check the ethanol label on the pump. This site is independent and not affiliated with Costco Wholesale Corporation.
