Is premium fuel worth the extra money?
What premium grades actually contain, the cars that benefit, and the break-even economy improvement you would need to justify the price.
6 min read · Written by Sam Richards · Last reviewed 2026-08-17
Key takeaways
- Premium grades combine higher octane with a heavier detergent additive package.
- You would need roughly 10-14% better economy to break even at typical price gaps — no ordinary engine delivers that.
- Cars specified for 98 RON, high-performance turbo engines and some direct-injection units are the genuine exceptions.
What you are buying
Premium petrol is usually 97-99 RON against 95 RON for standard unleaded, plus a stronger detergent package intended to keep injectors and inlet valves clean. Premium diesel offers a higher cetane number and similar cleaning additives.
The additive claims are real but modest. Modern standard fuels already meet detergency requirements, and the cleaning benefit shows up over long periods on engines with existing deposits rather than as an immediate change.
The break-even maths
If standard unleaded is 135p and premium is 150p, premium is 11% dearer. To be worth it purely on running cost, the fuel would have to deliver at least 11% better economy — around 5mpg on a 45mpg car.
Independent testing consistently finds gains of nought to three per cent on engines that are not tuned for higher octane. On those cars, premium is a net loss.
When it does make sense
Some performance engines have a minimum octane requirement in the handbook. Running them on 95 RON forces the ECU to retard ignition timing, which costs power and can cost economy — enough to make premium the cheaper choice per mile.
A periodic tank of premium can also be a sensible, cheap alternative to an injector cleaning service on an older direct-injection engine. As a habit for an ordinary car, it is money better spent on tyres and servicing.
Frequently asked questions
Does premium fuel improve fuel economy?
On engines not designed for high octane, testing typically shows gains of under 3% — far less than the 10-14% you would need to break even on the price.
Which cars need premium fuel?
Cars whose handbook specifies a minimum of 97, 98 or 99 RON — mostly performance and heavily turbocharged engines. Follow the handbook rather than the forecourt marketing.
Is premium diesel worth it?
Rarely for economy. It can be worth an occasional tank on a high-mileage engine for its detergent package, but as a routine purchase it does not pay for itself.
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Prices come from the UK Government's Competition and Markets Authority (CMA) open fuel price scheme and refresh throughout the day. Figures older than seven days are excluded.