E10 or E5: Which Petrol Should You Actually Be Using?

If your car was manufactured after 2011, you’ll almost certainly be fine using E10 petrol. It’s the UK’s standard unleaded fuel, it’s cheaper than super unleaded, and most modern engines are designed to run on it without issue.

However, there are exceptions. Some older vehicles shouldn’t use E10, and there’s ongoing debate about whether the potential mpg difference means E5 super unleaded can sometimes work out better value. This guide explains when each fuel makes sense.

What E10 and E5 actually are

Both are unleaded petrol. The number refers to the maximum percentage of ethanol blended into the fuel: up to 10% in E10, up to 5% in E5. Ethanol is an alcohol derived from plant material, typically sugar beet or wheat in the UK. It is blended into petrol partly to reduce the carbon intensity of transport fuel.

The UK switched from E5 to E10 as the standard petrol grade in September 2021. Since then, E5 has been available only as super unleaded, which is typically 97–99 RON compared with 95 RON for standard E10.

That distinction matters. E5 super unleaded differs from standard E10 in two separate ways: lower ethanol content and higher-octane rating. These are independent properties. A higher-octane rating only benefits an engine that is specifically designed or mapped for it. If your car’s handbook says 95 RON is fine, you gain nothing from 97 except a higher receipt.

Is your car compatible with E10?

The quickest way to settle this is the GOV.UK E10 compatibility checker. Enter your make, model and year and it gives a definitive answer. For most drivers, one visit is all this question requires.

The broad pattern: most petrol cars from 2011 onwards are E10 compatible. Pre-2002 vehicles are more likely not to be, particularly those with older rubber fuel hoses, certain seals, and carburettor components made from materials that degrade when exposed to higher ethanol concentrations over time.

Cars made between 2002 and 2011 are a mixed picture. Some are compatible, some are not. Do not guess. Check.

Classic and vintage cars are the most common exception. Many owners of pre-1992 vehicles use E5 or seek out ethanol-free fuel where available. If you own something with a carburettor and original rubber fuel lines, E10 is not a sensible default.

A brief note on motorcycles: E10 compatibility is not universal even on modern bikes. Riders should check their manufacturer’s guidance separately.

One thing to be clear about: an incompatible vehicle will not suffer immediate engine failure from a single tank of E10. The risk is degradation of certain materials over time, not sudden breakdown. If you accidentally fill an older car with E10 once, it is not an emergency. But do not make a habit of it.

Where the mpg difference actually shows up

Ethanol contains less energy per litre than pure hydrocarbon petrol. E10, with its higher ethanol content, therefore delivers marginally fewer miles per gallon than E5. The theoretical penalty is in the region of 1–2%.

In practical terms: a car returning 45 mpg on E5 might return roughly 44.3 mpg on E10. Over a year of typical UK mileage (around 7,400 miles according to Department for Transport figures), that is roughly 3–4 extra litres of fuel consumed.

Figures are illustrative based on a 1.5% efficiency difference at 45 mpg and 7,400 annual miles. Your result will vary with engine, driving style and conditions.

Now compare that against the price premium. E5 super unleaded typically costs 8–12p more per litre than standard E10. On a 55-litre fill, that is £4.40–£6.60 extra per visit. Over 52 weekly fills, the annual premium is in the range of £228–£343.

The annual fuel saving from E5’s marginally better efficiency, at current typical prices, recovers only a small fraction of that premium. For the vast majority of compatible modern cars, E10 is the cheaper option overall. The maths is not close.

When E5 actually makes sense

Older vehicles not compatible with E10:

If the GOV.UK checker or your manufacturer says your car is not E10 compatible, use E5. This is not a preference or an optimisation. It is the correct fuel for your car.

Classic and historic vehicles:

Particularly pre-1992 cars with original rubber fuel hoses and seals not designed for ethanol exposure. E5 reduces the risk of degradation, though it does not eliminate it entirely. Many classic car owners also use ethanol treatment additives as a further precaution.

Engines that require 97+ RON:

Some performance cars specify a minimum octane rating of 97 RON. For these, super unleaded is the right fuel. But be precise: this is an octane requirement, not an ethanol one. If your handbook says 95 RON is fine, paying for 97 does nothing useful.

Long-term storage:

Ethanol is hygroscopic. It absorbs moisture from the air. Fuel sitting in a tank for months can cause problems in engines not designed for it. E5, or ethanol-free fuel where available, is a reasonable precaution for any vehicle that sits unused over winter or between seasons.

Myths that will not survive contact with facts

“E10 damages modern car engines”

It does not. The compatibility concerns are about specific older materials — certain rubbers, metals and plastics in fuel systems of vehicles built before E10 was on the roadmap. Cars manufactured to E10 specification use components selected for compatibility. There is no mechanism by which E10 harms a compatible engine. The GOV.UK guidance on E10 is clear on this point.

“E5 noticeably improves performance in standard cars”

The marginal improvement in energy density is real but not perceptible in normal driving. You will not feel it. The difference between 95 RON and 97 RON only matters if your engine is mapped to exploit higher octane. Most standard engines are not.

“Supermarket E10 is lower quality than branded E5”

Grade and brand are separate things. A supermarket selling 95 RON E10 and a major oil company selling 95 RON E10 are both selling fuel that meets the same EN228 UK standard. Some premium branded fuels contain additional detergent additives, but that is a branding decision, not a function of ethanol content.

“Switching between E10 and E5 damages the engine”

For compatible vehicles, it does not. If your car takes E10 without issue, an occasional tank of E5 super unleaded, on a long motorway run, say, where it is the available grade, causes no harm at all.

E10 vs E5 at a glance

Pump price differential is illustrative. Check current prices before filling up.

Which one should you use?

Most drivers with a post-2011 car: Use E10. Check the GOV.UK tool once if you want certainty. After that, stop thinking about it.

Drivers with a pre-2002 vehicle or one flagged as incompatible: Use E5. It costs more, but the alternative carries a real risk of fuel system degradation over time.

Drivers with a performance car that specifies 97+ RON: Use E5 super unleaded, but because of the octane requirement, not the ethanol content. If your handbook says 95 RON is adequate, you are paying a premium for nothing.

Classic car owners: E5 is the safer choice. Consider an ethanol treatment additive if the car is stored for extended periods.

Cost-conscious drivers with a compatible modern car: Use E10 and put the saving towards finding the cheapest forecourt near you, which will outweigh the E5/E10 price difference regardless of how you do the sums.