Since September 2021, standard unleaded at UK pumps has been E10— petrol blended with up to 10% renewable ethanol. The “super” grade, typically 10–15p/L dearer, is E5: up to 5% ethanol and a higher octane rating. Which should you buy? For most drivers the answer is boringly simple; for two groups it genuinely matters.
What the labels mean
| E10 (standard unleaded) | E5 (super unleaded) | |
|---|---|---|
| Ethanol content | Up to 10% | Up to 5% |
| Octane (RON) | 95 | 97–99 |
| Typical price gap | — | +10–15p/L |
| Who needs it | Almost everyone | Incompatible or high-performance engines |
Group one: cars that shouldn’t use E10
Roughly 95% of petrol cars on UK roads are E10-compatible, but older vehicles — broadly, many built before 2011, and most classics — can suffer from ethanol’s habit of degrading rubber seals and attracting moisture. If that is your car, E5 is not a luxury; it is the correct fuel. Check yours in thirty seconds with the government’s official E10 checker.
Group two: engines that can exploit high octane
Some performance and turbocharged engines can advance ignition timing on 97–99 RON and extract a little more power or efficiency — if the manufacturer says so. For everything else, higher octane is simply money spent on a number your engine never uses. A typical family car gains nothing measurable from super unleaded.
The economy wrinkle
Ethanol contains less energy than petrol, so E10 delivers fractionally worse fuel economy — around 1% for most cars, occasionally more for small engines on short trips. At a 10p+ price gap, E5 never pays for itself on economy alone: 1% of a 150p litre is 1.5p, not 12p. The arithmetic only flips if your engine specifically benefits from octane.
The verdict
- Modern everyday car: E10, always — and spend your attention on where you buy instead: the same E10 varies by 10p+ between stations near you (check yours).
- Pre-2011 or classic: E5, as a compatibility matter.
- Performance engine with a manufacturer recommendation: E5/super if you want what you paid for.