E10 vs E5 petrol

The difference in one line

E10 is standard unleaded petrol with up to 10% renewable ethanol, rated 95 RON. E5 is super unleaded with up to 5% ethanol, usually 97–99 RON. The number after the E is the ethanol cap, not the octane rating — a common source of confusion.

E10 became the standard grade at UK forecourts in September 2021, replacing the previous E5 standard. E5 did not disappear: it remained available as the premium "super" grade, which is why every forecourt still sells both.

What each grade costs today

Across the 1,471 forecourts publishing an E10 price and the 1,092 publishing E5, the UK averages are 173.3p and 189.7p respectively — a premium of 16.4p a litre, or £9.02 on a 55-litre tank. A driver filling up fortnightly on super unleaded spends about £235 a year more than one using standard unleaded.

Note that far fewer forecourts stock E5 than E10, so if your car genuinely requires super unleaded it is worth checking availability on the map before a long trip.

Which one does your car need?

Check the fuel filler flap and the handbook. If either specifies a minimum octane rating of 97 or 98 RON, use E5. If it says 95 RON — which covers the overwhelming majority of petrol cars on UK roads — E10 is the right fuel and super unleaded offers no benefit.

The exceptions worth knowing about:

• Classic and pre-2000 vehicles. Ethanol attacks some older fuel system components. Stay on E5.
• Some early-2000s models. A small number were never approved for E10. Check the government's E10 vehicle checker if yours is from that era.
• Performance engines. High-compression and turbocharged engines tuned for 98 RON can lose power and efficiency on 95 RON. Follow the handbook.
• Mopeds, garden machinery and marine engines. Many are not E10 approved and are often left standing for months, when ethanol's tendency to absorb moisture causes the most trouble.

E10 and fuel economy

Ethanol has a lower energy density than petrol, so a litre of E10 carries slightly less energy than a litre of E5. In practice that means roughly a 1% reduction in miles per gallon — small enough that most drivers never notice it, and far too small to offset a premium of several pence a litre.

The honest summary: unless your handbook tells you otherwise, buy the cheapest E10 you can find. Finding a forecourt 5p a litre cheaper saves you far more than any grade choice — which is what the town-by-town price pages are for.