Branded fuel vs supermarket fuel: is it worth it?

Every litre of standard unleaded sold in the UK, whether it comes from a supermarket forecourt or a big oil company's station, has to meet the same British Standard. The difference between them is the additive package mixed in on top, not the fuel underneath — so for most ordinary cars, the price on the totem sign matters far more than the badge above it.

The law decides what goes in the tank, not the brand

What can be sold as petrol or diesel in the UK is set out in law, in the Motor Fuel (Composition and Content) Regulations 1994 and later amendments, published on legislation.gov.uk. Retailers do not get to write their own rules about it.

Unleaded petrol is specified against the British Standard BS EN 228, published by BSI, which covers the requirements and test methods for automotive unleaded petrol. Diesel has its own equivalent standard.

That means a supermarket cannot legally sell you something weaker or thinner than the standard allows. If it is sold from a pump marked unleaded, it meets the same specification as the unleaded at the branded station down the road.

Octane is part of that specification too. Standard unleaded in the UK is usually 95 octane; the "super" or "premium" grades are typically 97 to 99. That is a real, printed difference — unlike marketing claims, it is on the pump.

What branded fuel actually adds

The honest answer is: detergents and other additives, blended in above the legal minimum, in a recipe each company keeps to itself.

These are real products. Whether they make a measurable difference to fuel economy, engine cleanliness or emissions in everyday British driving is a different question, and one where the evidence you will find online is mostly published by the people selling the fuel.

We could not find any UK regulator or government finding that settles it either way. So we are not going to tell you branded fuel is a waste of money, and we are not going to tell you it will transform your car. What we can tell you is this:

• Both meet the same statutory standard, so neither is "bad" fuel.
• The extra you pay per litre is certain. The benefit is not.
• Your car's handbook, or the label inside the fuel flap, tells you the minimum octane the manufacturer requires. Follow the handbook, then buy the cheapest fuel that meets it.

If your handbook says 95 octane, a 95 octane supermarket unleaded is the fuel your manufacturer designed the car around.

E10, E5 and the one time the dearer pump is the right call

Standard petrol in the UK is E10, meaning it contains up to 10% renewable ethanol. The Department for Transport moved Great Britain to E10 as the standard grade in September 2021, and Northern Ireland followed later, in 2022.

Most cars are fine with it. Some older and classic vehicles are not, and running them on E10 can damage seals, hoses and other parts over time.

There is a free official checker on GOV.UK — the E10 petrol vehicle compatibility service — where you enter your make, model and year. It costs nothing and takes a minute.

Super unleaded has generally stayed at the lower E5 blend, which is why owners of older vehicles are often told to use it. If that is you, buying the dearer pump is a compatibility decision, not a performance upgrade. Do not let anyone sell it to you as both.

Where your money actually goes at the pump

A big chunk of what you hand over is tax, and it is identical at every forecourt in the country.

Fuel duty is charged at the same rate per litre wherever you buy, and VAT at 20% is then charged on top of the pump price including that duty. No retailer, branded or supermarket, can undercut another on the tax.

So the whole of the price gap you see between two stations comes from the cost of the fuel itself, the additives, and the retailer's margin. That last one is where the real money for you sits.

The Competition and Markets Authority looked hard at this in its road fuel market study and concluded that competition between forecourts had weakened and retailer margins had widened. The government's response was to legislate: the Motor Fuel Price (Open Data) Regulations 2025 set up a scheme, known as Fuel Finder, requiring retailers to report their pump prices so drivers and comparison services can see them. Check GOV.UK for the current start date, as the scheme is being phased in.

The practical point for you today: prices for the same specification of fuel vary street by street, and that variation is usually worth more than any additive debate.

Your handbook, or the fuel flap, tells you what the engine actually needs.

If you think the fuel damaged your car

Fuel is "goods" in law, so under the Consumer Rights Act 2015 it has to be of satisfactory quality and fit for purpose. That applies to supermarket and branded forecourts alike.

If you suspect contaminated or wrong fuel:

1. Stop driving the car if it is running badly. Do not keep going in the hope it clears.
2. Keep the receipt, note the time and the pump number, and if you safely can, keep a sample.
3. Complain to the retailer in writing first, and give them a chance to put it right.
4. If they refuse, get free consumer advice. Fuel quality and pump measures are enforced by local authority Trading Standards.

In England and Wales you report it through the Citizens Advice consumer service, in Scotland through Advice Direct Scotland at consumeradvice.scot, and in Northern Ireland through Consumerline. They pass reports on to Trading Standards.

Questions people ask

Does supermarket fuel damage engines?

There is no regulator finding that supermarket fuel damages engines, and it must meet the same British Standard as any other unleaded or diesel. If a car has a fault after filling up anywhere, treat it as a possible contaminated batch and report it, rather than assuming the brand is the cause.

Is super unleaded worth it in an ordinary car?

If your handbook asks for 95 octane, super unleaded is giving you something the engine was not designed to need. The exception is an older or classic vehicle that needs the lower-ethanol E5 blend.

Does branded fuel give better miles per gallon?

We have not found an independent UK source that shows a reliable economy gain in normal driving. Your driving style, tyre pressures and the weight in the boot are things you can measure and change for nothing.

Is diesel from a supermarket the same as branded diesel?

The base diesel must meet the same standard, with additive packages varying by supplier. As with petrol, check what your manufacturer specifies and then buy on price.

Why do two stations a mile apart charge such different prices?

Tax is identical, so the difference is the retailer's costs and margin, plus local competition. That is exactly what the Competition and Markets Authority raised, and why the open data scheme was brought in.

What to do next

• Compare pump prices near you before you fill up on our cheapest fuel page — a few pence a litre, every week, adds up faster than any additive.
• Check your car's minimum octane in the handbook, and if it is older, run the free GOV.UK E10 compatibility check.
• Keep the rest of your motoring costs on a leash with MOT, tax and insurance reminders.
• If money is tight and fuel is the bill you are squeezing, get free help from National Debtline on 0808 808 4000, StepChange or Citizens Advice, and see help with debt. Never pay a fee for debt advice.

Where this comes from

• The Motor Fuel (Composition and Content) Regulations 1994
• Check if your vehicle can use E10 petrol (GOV.UK service)
• Empowering drivers and boosting competition in the road fuel retail market: government response
• The Motor Fuel Price (Open Data) Regulations 2025: impact assessment
• BS EN 228 Automotive fuels. Unleaded petrol. Requirements and test methods (BSI)
• Consumer Rights Act 2015
• Citizens Advice: consumer advice and complaints
• Tax on shopping: fuel duty (GOV.UK)