Is Costco Fuel Good? UK Petrol and Diesel Quality, Who Supplies It, and How It Compares With Shell V-Power

Costco petrol is usually some of the cheapest in the area, and cheap fuel makes people wonder what they are putting in the tank. If you want to know whether Costco fuel is good quality, who actually supplies it, and whether it is any worse than Shell V-Power or BP Ultimate, this post sets out what the standards say, what Costco claims, and what nobody has published.

Short answer: Yes. Costco fuel meets the same legal standards as any UK forecourt. Every litre of road petrol and diesel sold in Great Britain has to meet the same legal standards, BS EN 228 for petrol and BS EN 590 for diesel, whether it comes from Costco, a supermarket or Shell. On top of that, Costco says its Kirkland Signature Unleaded, Premium Unleaded 97 and Premium Diesel contain "powerful deep-cleaning fuel additives". Costco does not say who supplies the base fuel.

What standard does UK petrol and diesel have to meet?

UK road fuel is regulated by law, not by brand. The Motor Fuel (Composition and Content) Regulations 1999 set the rules for petrol and diesel sold in Great Britain. As amended in 2021, they refer to two British Standards (SI 2021/199):

The standards cover things like octane, sulphur, vapour pressure, density, cetane, water and how much ethanol or biodiesel the fuel can contain. A forecourt cannot sell "budget" petrol that falls short of them.

The AA has made the same point. As quoted in the press, an AA spokesperson said fuel quality "is governed by the same European standard, whether it is sold at a supermarket in Manchester (or) an independent outside Mevagissey."

So the floor is the same at Costco as anywhere else. Where fuels differ is octane grade and the additive package added on top.

Is there a Top Tier fuel standard in the UK?

No. Top Tier is a voluntary, carmaker-written detergent standard used mainly in the Americas. Its licensed brands list covers markets including the USA, Canada, Mexico, Japan and several Latin American countries, but not the UK or anywhere in Europe.

That matters because a lot of "is Costco fuel good" answers online come from the US, where Costco's gas is Top Tier licensed (our US Top Tier post covers that). None of that applies to a UK forecourt. In the UK there is no independent badge that ranks one brand's additives above another's. Each brand makes its own claims about its additive pack.

What fuel does Costco sell in the UK?

Costco's Kirkland Signature fuel page names three fuels:

Older Costco UK posts and member forums mention a 99 octane premium. The current Costco page says 97, so treat 97 as the figure today and check the pump.

In our data, 22 of Costco's UK warehouses have a petrol station, and all 22 sell unleaded, super unleaded and diesel. Warehouses such as Hayes, Chingford, Croydon and Wembley do not have one. The full list is on our Costco petrol stations page, and opening times are on Costco petrol opening times.

Who supplies Costco fuel in the UK?

Costco does not say. We could not find any statement from Costco UK, or any trade press report, that names the company supplying its base petrol and diesel.

Here is what we found, and how much weight each piece deserves:

• Costco's own page describes the additives but names no refiner or wholesaler.
• Fuel price sites say only that Costco buys from refineries and distributors. PetrolPrices puts it as: "Costco buys its petrol and diesel from refineries and distributors across the UK."
• One price site says Costco sources fuel from "trusted suppliers, including Valero Energy". It gives no source, and we could not confirm it. Valero does run the Pembroke refinery and supplies UK forecourts, for example 115 Co-op sites, but that is not evidence about Costco.
• Forum sightings are anecdotal. A Mercedes owner on MBClub UK wrote in 2017 that he saw a Greenergy tanker at a Costco forecourt. One tanker on one day does not tell you who supplies all 22 sites now.

What we can say with confidence is how UK fuel supply generally works. Most retailers, supermarkets included, do not refine their own fuel. They buy from refiners and wholesalers who draw on the same terminals, and the finished fuel must meet BS EN 228 or BS EN 590 whoever buys it. The brand difference is mostly the additive. Our post on where Costco gets its fuel in the US explains the same idea for the American supply chain, but its supplier facts are US-only.

What additives are in Costco fuel?

Costco's UK fuel page says all three fuels contain "powerful deep-cleaning fuel additives" that keep "your engine protected and running like new". Its specific claims:

• The additive "helps to remove existing deposits on petrol engine intake valves, and prevents new deposits" from forming.
• It fights "existing injector deposits and prevents new deposits from forming", which Costco ties to fuel economy.
• It restores power "by removing deposits from fuel injection equipment".
• Cleaner engines reduce "exhaust pollution caused by valve deposits and plugged fuel injectors".

What Costco UK does not publish:

• The name or supplier of the additive.
• A dose, such as the "five times the minimum" figure Costco uses in the US.
• Any independent test of its UK fuel.

So the additive claims are Costco's own. They are the same kind of claims every fuel brand makes, and none of them has been tested head to head against other UK brands in public.

Is Costco Premium Diesel good?

It is a legal BS EN 590 diesel with Costco's cleaning additive. Beyond that, Costco publishes very little about it.

"Premium diesel" is a marketing term, not a separate legal grade. Brands such as Shell (V-Power Diesel) and BP (Ultimate Diesel) sell premium diesels with extra additives and, in some cases, a higher cetane number. Costco's current fuel page gives no cetane figure; the only one on record is a minimum of 51, the EN 590 floor, from a 2022 customer reply. It does not say how its Premium Diesel differs from a standard B7 diesel apart from the additive.

Members on car forums report mixed impressions. Some say their car feels smoother; others notice no difference from supermarket diesel. Neither is evidence either way. Our Costco diesel UK post covers the cetane figure Costco has given and how it compares with V-Power Diesel and BP Ultimate Diesel.

Premium Diesel is the only diesel Costco sells in the UK, so it is the price you see on our Costco diesel price page. On 15 October 2026, the average Costco diesel price across our 22 stations was 190.4p/L, a median 25p/L above unleaded at the same site.

How does Costco fuel compare with Shell V-Power or BP Ultimate?

Shell V-Power and BP Ultimate are branded premium fuels. They do two things that standard fuel does not:

1. Higher octane. Shell V-Power petrol is rated 99 RON in the UK (Wikipedia), against 95 for standard unleaded and 97 for Costco Premium Unleaded. UK super grades must be at least 97 RON.
2. A stronger, proprietary additive pack. Shell markets V-Power on cleaning and friction-reducing additives. BP does the same with Ultimate. These are the brands' own claims, backed by their own testing.

Here is how the options line up on what is published:

Does the extra octane help? Only if your engine can use it. Which? says there is "usually little benefit" to super unleaded "unless you drive a high-performance or imported car" (Which?). An older Which? Car test, reported by Fleet News, found small gains in some turbo engines and concluded that for many cars paying more for super fuels was a waste of money.

On additives, nobody has published a UK test that ranks Costco against Shell, BP or Esso. Anyone who tells you Costco fuel is clearly worse, or clearly as good as V-Power, is going beyond the evidence.

The difference you can measure is price. Which? puts the usual super unleaded premium at 10–15p a litre more than unleaded. At Costco the gap is smaller: in our 15 October 2026 reading, Costco Premium Unleaded was a median 10p/L above Costco Unleaded at the same site, with a range of 7p to 16p. For how Costco's prices compare with the UK average and the supermarkets, see is Costco fuel cheaper.

Is Costco E10 or E5?

Costco's standard unleaded is E10, and its Premium Unleaded is the E5 super grade.

That is the law, not a Costco choice. The government made E10 the standard 95 octane petrol in Great Britain from 1 September 2021, and required the higher-octane super grade to stay E5 as a "protection grade" for older vehicles. According to the government's E10 guidance, around 95% of petrol vehicles on the road can use E10, and Northern Ireland switched in November 2022. "Diesel fuel has not changed."

The government said it would review the E5 protection grade after five years. We have not found a published outcome of that review as of October 2026.

If your car is not E10 compatible, use Costco Premium Unleaded 97. You can check your car with the government E10 checker.

Will Costco fuel damage your engine?

No. The common worries do not hold up:

• "Cheap fuel is lower quality." Costco's low price comes from its members-only, high-volume model and thin margins, not a lower fuel spec. The base fuel must meet BS EN 228 or BS EN 590 like everyone else's.
• "It's watered down." Fuel standards set limits on water, and water in fuel would damage engines. We found no evidence of Costco selling watered-down fuel.
• "It will void my warranty." Carmakers specify an octane rating and, for petrol, whether the car can use E10. They do not require a brand. Costco sells both 95 and 97 octane petrol.
• "Supermarket-style fuel has no additives." Costco says all three of its UK fuels contain a cleaning additive.

Contaminated deliveries can happen at any forecourt, branded or not. If your car starts badly straight after filling up anywhere, keep the receipt and contact the site. For a longer look at the US version of these myths, see is Costco gas bad for your car.

Should you fill up at Costco?

For most cars, yes. If your car takes standard unleaded, Costco Unleaded meets the same legal standard as any other forecourt, carries a cleaning additive, and usually costs less. Buy Premium Unleaded 97 if your car needs 97+ octane or is not E10 compatible. If you drive a performance car that asks for 99 RON, Costco's premium is lower than V-Power, so check your handbook.

You do need a Costco membership to use the pumps (who can fill up at Costco). Find your nearest site with Costco petrol near me, or check today's prices at a station such as Watford, Birmingham, Manchester or Thurrock (Lakeside). All UK prices are on the Costco UK fuel hub. For Costco fuel quality in Australia, see is Costco fuel good in Australia.