E10 Petrol: Is It Costing You More Than You Think?

What actually is E10?

The "E" stands for ethanol and the "10" is the percentage. E10 petrol is standard unleaded blended with up to 10% bioethanol — a renewable alcohol made from fermenting crops such as wheat, sugar beet and waste wood.

Before September 2021, UK pumps dispensed E5 petrol, which contained up to 5% ethanol. The government doubled the blend to help meet climate targets. The idea is simple: ethanol is partly carbon-neutral because the crops absorb CO₂ as they grow, offsetting some of what's released when the fuel is burned.

The switch was estimated to cut UK transport CO₂ emissions by around 750,000 tonnes per year — roughly the equivalent of taking 350,000 cars off the road. E10 was already standard in countries like France, Germany, Finland, Belgium, the US and Australia before the UK adopted it.

How does E10 affect your fuel economy?

This is the question most drivers care about — and the answer is that yes, E10 does reduce your miles per gallon. Ethanol contains around a third less energy per litre than pure petrol. When you blend it at 10%, the overall energy content of the fuel drops, meaning your engine needs to burn slightly more to produce the same power.

The UK Government's official estimate is a reduction of around 1%. The RAC and the US Energy Information Administration put it at up to 3%. In practice, most drivers report a drop somewhere in the 1–2% range — enough to measure on a spreadsheet, but not enough to notice on a single journey.

Your car's engine management system adjusts the fuel-air ratio automatically to compensate for the lower energy content, so you won't feel any loss of power. You'll just visit the pump very slightly more often.

What does that look like in pounds and pence?

Let's put some real numbers on it. Say you fill a 50-litre tank once a week at the current average of around 156p per litre. That's £78 per fill-up.

• At 1% efficiency loss: You're using an extra 50p of fuel per tank — about £26 per year.
• At 2% efficiency loss: That's roughly £1 extra per tank — around £52 per year.
• At 3% efficiency loss: About £1.50 extra per tank — roughly £78 per year.

For most drivers, the real-world cost is somewhere between £30 and £75 per year. That's noticeable across a full year, but far less than the difference between filling up at a cheap supermarket versus an expensive branded station.

Should you use premium E5 instead?

E5 super unleaded (97+ octane) is still available at most filling stations and contains only 5% ethanol. It gives marginally better fuel economy — but it costs significantly more.

E5 super unleaded typically costs 8–12p per litre more than standard E10. On a 50-litre fill-up, that's an extra £4 to £6 per tank. Over a year of weekly fills, you'd spend around £200 to £300 more on fuel.

The MPG benefit of E5 over E10 recovers at most about £75 of that premium — meaning you'd still be £125 to £225 worse off per year by choosing E5. The maths simply doesn't work for the vast majority of drivers.

What about premium branded fuels like Shell V-Power?

Fuels like Shell V-Power Nitro+, BP Ultimate, Esso Synergy Supreme+ and Tesco Momentum 99 are all E5 fuels with higher octane ratings (typically 97–99 RON) and proprietary cleaning additives.

These fuels genuinely do contain additive packages designed to keep fuel systems cleaner. However, unless your car is specifically tuned for high-octane fuel, the performance and economy benefits are minimal in everyday driving. Modern engines are designed and tested to run perfectly well on 95 RON E10.

If you drive a standard family car, you're paying a significant premium for a marginal benefit. The money would be better spent on proper tyre pressures and smoother driving habits.

Is your car compatible with E10?

The overwhelming majority of cars on UK roads can use E10 without any issues. All petrol cars manufactured since 2011 are guaranteed to be compatible, and most cars built from the late 1990s onwards are also approved.

However, the Department for Transport has estimated that around 700,000 vehicles on UK roads are not compatible with E10. These are mainly older, classic and some early 2000s models. Some notable examples include:

• Volkswagen: Some older Golf models (pre-2005 with certain direct injection engines)
• Mazda: Some early MX-5 models
• Vauxhall: Vectra, Signum and Zafira models with the 2.2-litre direct-injection petrol engine
• Mercedes: C200 CGI and CLK 200 CGI (2002–2005)
• Toyota: Avensis 2.0L with 1AZ-FSE engine (2000–2008)
• Rover: All models (no compatibility data available as the manufacturer no longer trades)

If you're not sure, the simplest option is to use the Government's free E10 vehicle checker. Enter your car's make and model and it will tell you straight away.

What damage can E10 cause in older cars?

Ethanol is both hygroscopic (it absorbs water from the air) and a solvent. In cars that weren't designed for it, this can cause several issues:

• Corrosion: Water absorbed by the ethanol can corrode aluminium, zinc, brass, copper and lead/tin-coated steel components in the fuel system.
• Seal and gasket damage: Ethanol can degrade rubber seals, hoses and gaskets — potentially leading to fuel leaks.
• Deposit build-up: Ethanol's solvent properties can dislodge existing deposits in the fuel system, which then block carburettor jets and fuel injectors.
• Fuel degradation in storage: E10 goes stale faster than E5. In a sealed container it may last up to 12 months, but in a half-full tank or unsealed can it can degrade within 3 months — a real issue for classic cars and seasonal vehicles.

For classic car owners, the Federation of British Historic Vehicle Clubs recommends replacing all rubber fuel system components with ethanol-resistant parts, and using E5 super unleaded or specialist ethanol-free storage fuels wherever possible.

E10 and garden equipment, motorcycles and boats

It's not just older cars that can struggle with E10. Many lawnmowers, strimmers, chainsaws, generators and small marine engines were not designed for higher ethanol blends. Motorcycle compatibility varies — most current models are fine, but older bikes may not be.

The key issue is storage. Garden machinery often sits idle for months over winter with fuel in the tank. E10 absorbs moisture during this time, which can cause phase separation — where the ethanol-water mixture drops to the bottom of the tank, leaving low-octane petrol floating on top. This can make engines difficult or impossible to start, and can cause internal corrosion.

Does E10 actually help the environment?

The environmental case for E10 is real but nuanced. The government's estimate of a 750,000-tonne annual CO₂ reduction is based on the fact that ethanol's carbon is partly offset by the crops that produced it absorbing CO₂ as they grew.

However, critics point out that this doesn't account for the full lifecycle — the energy used to farm, harvest, transport and ferment the crops. When you factor in land use changes and the fact that some ethanol feedstocks compete with food production, the net benefit is smaller than headline figures suggest.

There are also localised air quality concerns. While E10 reduces CO₂, the AA has noted that it does not improve local air quality — and some studies suggest a slight increase in pollutants such as particulates and nitrogen oxides.

That said, E10 is widely seen as a pragmatic stepping stone while the transition to electric vehicles continues. For the millions of petrol cars still on UK roads, even a modest emissions reduction per vehicle adds up.

Quick summary: E10 vs E5

What should most drivers do?

For the vast majority of UK drivers — anyone with a car built after 2011, and most cars from the late 1990s onwards — the answer is straightforward: stick with E10. The fuel economy penalty is real but small, and it's far outweighed by the higher cost of E5 super unleaded.

Where you buy your fuel matters far more than which grade you choose. Prices can vary by 20p or more per litre between stations just a few miles apart. Finding a cheaper station will save you far more over a year than any fuel grade switch ever could.

If you drive a classic car, an older model that isn't E10 compatible, or equipment that sits idle for long periods, then E5 super unleaded is the right choice — and it's worth factoring the higher cost into your running expenses.