Is premium fuel worth paying extra for?
What the higher octane number actually does, the small number of cars that genuinely benefit, and why supermarket fuel is not the poor relation people assume.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 4 min
Short answer
For most ordinary cars, premium fuel does not produce enough benefit to justify the price difference — the higher octane rating prevents knock in engines that need it, and if your car does not need it, the engine cannot use it. It is worth it if your handbook specifies a minimum octane above standard, or if your car is turbocharged and high-performance. All fuel sold in the UK, supermarket included, meets the same British Standard.
Octane rating measures a fuel's resistance to detonating on its own under compression rather than burning when the spark says so. That uncontrolled detonation is knock, and it damages engines. A high-performance engine with high compression or a lot of boost is designed around fuel that resists it, and running such an engine on standard fuel makes its management system retard the ignition timing to protect it — which costs power and, over time, some efficiency. An ordinary engine designed for standard 95 octane cannot make use of the extra resistance, because it was never going to knock in the first place.
Step by step
- Read the handbook and the fuel filler flap.This answers the question directly. If it says a minimum of 95 RON, standard unleaded is what the engine was designed around. If it specifies 97 or 98 RON, or says premium recommended, the engine will use it. Anything described as required rather than recommended should be followed.
- Understand what the premium grades actually offer.Two things: a higher octane number, and a different additive package aimed at keeping injectors and inlet valves clean. The octane part only helps engines that need it; the detergent part is a genuine but modest benefit on any engine, and mainly matters on direct-injection engines that are prone to inlet deposits.
- Ignore the supermarket fuel myth.All petrol and diesel sold in the UK must meet the same British Standard, and it usually comes from the same terminals. What differs between brands is the additive package, not the base fuel. Supermarket fuel is not lower quality; it is standard fuel with a standard additive dose.
- Test it properly if you want to know.If you are curious about your own car, run three tanks of standard, measuring brim-to-brim, then three of premium. Anything less than that is swamped by variation in driving, weather and traffic. Most people who do this find the difference is far too small to pay for.
- Consider an occasional tank of premium for a specific reason.On a direct-injection car that does a lot of short journeys, an occasional tank with a stronger detergent package is a reasonable cheap precaution. It is not a fix for a fault and it will not clear a genuinely blocked injector.
- Do not use premium diesel expecting more power.Premium diesel is about cetane rating and additives rather than power. Any effect is modest, mostly around cold starting and cleanliness, and it does not transform a car.
- Check what the E10 change means for your car.Standard UK petrol is E10, containing up to ten per cent ethanol. Super unleaded grades are generally still E5. Almost every petrol car built since 2011 is E10 compatible, but some classic and older vehicles are not, and for those, super unleaded is the practical answer rather than a performance choice.
Common mistakes
- Buying premium as a treat for an ordinary car — An engine designed for 95 RON cannot extract more energy from higher-octane fuel. The energy content is essentially the same; only the knock resistance differs.
- Avoiding supermarket fuel on principle — It meets the same standard and usually comes from the same refinery and terminal. The saving is real and the difference is not.
If it doesn't work
Car pinks or knocks under load on standard fuel
Cause: The engine is finding standard octane marginal — Fix: Try premium. Genuine knocking on a car that specifies 95 RON also warrants investigation — carbon build-up, a sensor fault or overheating can all cause it.
Older car and standard petrol is now E10
Cause: Ethanol content can affect older fuel system components — Fix: Check whether your vehicle is E10 compatible on the GOV.UK checker. If not, use super unleaded, which is generally E5.
Noticeable difference on premium in a performance car
Cause: The engine management is able to run more advanced timing — Fix: That is exactly the case where premium is worth it. Follow the handbook rather than the price.
Fuel economy seems better on premium
Cause: Possible on an engine that benefits, but easily confused with driving variation — Fix: Measure over several tanks brim-to-brim before concluding. Even where there is a real gain, it has to exceed the price premium to be worth having.
Questions people ask
Does premium fuel clean my engine?
The detergent packages do help keep injectors and, on port-injected engines, inlet valves clean. It is a maintenance benefit rather than a performance one, and it is gradual. It will not undo an existing problem.
What is E10 and does it affect economy?
E10 is petrol containing up to ten per cent ethanol, which became the standard grade in Great Britain in 2021. Ethanol has slightly less energy per litre, so a very small reduction in economy is expected — typically around one per cent, which is far smaller than the variation caused by driving style.
My car says premium recommended, not required. What should I do?
Recommended means the engine has been calibrated to take advantage of it but will run safely without. You will get slightly less performance on standard fuel and no damage. It is a genuine choice, unlike required.