In Britain the petrol decision is a two-way one: standard E10 at 95 octane, or E5 super unleaded at 97 octane and above. Every forecourt that sells two petrol grades sells exactly this pair. The interesting question is not which is better — it is whether you are one of the drivers who has to buy the dearer one.

What Actually Separates the Two Grades

Two things, and they travel together. E10 contains up to 10% renewable ethanol; E5 contains no more than 5%. E10 is the 95 octane grade; E5 is the ‘super’ grade at 97+ octane. Octane is a measure of resistance to pre-ignition, not of energy content or quality, which is why a higher number is only useful to an engine designed to exploit it.

On economy, GOV.UK is measured: using E10 can slightly reduce fuel economy, and you may see a reduction of around 1%, but it is unlikely to be noticeable in everyday driving. Hold that 1% next to the price gap below and the arithmetic answers itself for most drivers.

The Price Gap We Measure

On 16 August 2026 we measured both grades across the roughly 3,900 UK stations in our data. E10 averaged 160.4p per litre. Super unleaded, which we found priced at 2,849 of those stations, averaged 177.9p. That is a gap of about 17p per litre — on a 50-litre fill, roughly £8.75 more for the same journey.

Two caveats worth stating plainly. First, this is our own data across the stations we track, not a national statistic. Second, super is not sold everywhere: about a quarter of the stations in our set had no super unleaded price at all, which matters if your vehicle needs it and you are planning a route through rural areas.

When You Should Be Buying E5 Super

There is one clear case, and it is not about performance. GOV.UK states that around 95% of petrol-powered vehicles on the road are compatible with E10 and that all new cars manufactured since 2011 are compatible — but that classic and older vehicles, some specific models from the early 2000s, and some mopeds, particularly those at 50cc and under, may not be. For those vehicles the advice is explicit: continue to use E5 in the ‘super’ grade at 97+ octane. Check yours with the government’s free E10 vehicle checker, and if the model is not listed — common for classic cars — GOV.UK advises staying on E5.

The second case is a manufacturer requirement. Some engines are specified for a minimum octane above 95. Your handbook, not a forecourt sign, is the authority on that. If it calls for a higher octane, the super grade is the correct fuel and the premium is simply part of running the car.

When the Premium Is Buying You Nothing Obvious

If your car is E10-compatible and its handbook does not call for a higher octane, the 17p we measure is a discretionary spend. Manufacturers and retailers make various claims for premium fuels; we do not measure engine outcomes and will not repeat figures we cannot check. What we can say with confidence is the price side, and it is stark: the gap between two brands selling ordinary E10 is often the same order of magnitude as the gap between E10 and super at a single station.

On our data the mean E10 price ran from 152.9p at Sainsbury’s to 162.0p at BP — a 9p spread between brands, before you have chosen a grade at all. Switching where you fill up is usually the bigger lever than switching what you fill up with. Our guide to saving on fuel works through the rest.

Mixing, Switching and Mistakes

If your vehicle is E10-compatible, GOV.UK says there is no reason you cannot mix the two grades, and that filling up with E5 when E10 is not available is perfectly safe. If you put E10 into a non-compatible vehicle, the advice is to fill up with E5 next time; unlike petrol in a diesel engine you should not need to drain the tank, and a single tank will not damage the engine. Prolonged use in a non-compatible vehicle, however, may cause harm and is not recommended.

For the full picture on all three UK grades, including diesel, see our fuel types explained guide.