Guide
Is supermarket fuel bad for your car?
The idea that supermarket petrol is lower quality or harmful is one of motoring's most repeated myths. Here is what is actually in the tanker, and the small grain of truth behind the story.
Ask around and someone will tell you, with total confidence, that supermarket petrol is watered down, lower quality, or bad for your engine. It is one of the stickiest myths in British motoring, and it costs people money, because it talks them out of the cheapest fuel on the forecourt. The truth is more boring and more reassuring. Supermarket fuel is the same fuel.
Where supermarket fuel actually comes from
All petrol and diesel sold in the UK, supermarket or branded, has to meet the same British and European standard, BS EN 228 for petrol and BS EN 590 for diesel. It is refined in the same refineries and stored in the same regional fuel terminals, and the tanker that fills a supermarket forecourt often loads from the very same terminal as the one bound for a big name station down the road. There is no separate, inferior supply chain for the cheap stuff. The base fuel in your tank is to the same specification wherever you buy it.
The one real difference
Here is the grain of truth the myth grew from. Fuel brands add their own detergent and additive packages to the base fuel, and the premium branded grades add more of them than a standard supermarket fuel does. So it is fair to say a tankful of a premium branded fuel carries a richer additive mix than a tankful of basic supermarket unleaded. What is not fair is the leap from there to harmful. All UK fuel must contain enough detergent to keep an engine clean to the legal standard. Supermarket fuel clears that bar. It is not stripped back or dangerous, it simply carries the standard additive level rather than a premium one.
So will it harm your engine?
No. For an ordinary car running ordinary miles, supermarket petrol and diesel are completely fine, and millions of cars run on nothing else for their whole lives without trouble. The occasional report of a bad batch makes the news precisely because it is rare, and bad batches have come from branded stations too. Quality control applies across the board. If anything, a supermarket forecourt with high turnover is selling fresh fuel that has not been standing in the tank for long.
When a premium fuel might earn its place
There is a sensible middle ground. If you drive an older car with a lot of miles on it, running the occasional tank of a premium branded fuel can help clear deposits, thanks to those heavier detergents. That is a cheap once in a while service, not a reason to pay the premium every week. And if your handbook asks for a specific higher octane fuel, follow it. For everyone else, the everyday supermarket fuel is the right call, and our guide on whether premium fuel is worth it goes into when the dearer stuff actually pays.
The bottom line
Supermarket fuel is not bad for your car. It meets the same standard as every other forecourt and comes from the same supply. The real difference is the additive mix, which matters only at the margins and only for some cars. So buy with confidence, and choose on price. Put your postcode into the price finder to see which forecourts near you, supermarket or not, are cheapest today.
Common questions
Is supermarket petrol lower quality than branded fuel?
No. All UK petrol and diesel must meet the same British and European standard and is refined and stored in the same places. The base fuel is identical in specification. The only difference is the additive package, where premium branded grades carry more detergent than standard supermarket fuel, which does not make supermarket fuel harmful.
Will supermarket fuel damage my engine?
No. For a normal car it is completely fine, and millions of cars run on supermarket fuel for life without issue. It meets the legal detergent standard that keeps an engine clean. Rare bad batches have come from branded stations too, so quality control is not a supermarket problem.
Is branded fuel better than supermarket fuel?
Branded premium grades carry a heavier additive package, which can help an older high mileage car as an occasional clean, and some engines need a specific higher octane. For an ordinary modern car the everyday difference is too small to matter, so supermarket fuel is the better value choice.
Where does supermarket fuel come from?
From the same refineries and regional fuel terminals as branded fuel. The tanker filling a supermarket forecourt often loads at the same terminal as one bound for a big name station. There is no separate lower grade supply for supermarkets.