E85: the high-ethanol fuel blend explained
E85 is a fuel blend of up to 85% ethanol and 15% petrol, used only in flex-fuel vehicles. It usually costs less per litre than petrol, but a car burns more of it to go the same distance, so it isn't always cheaper to run.
In this entry
What E85 is — definition, ethanol percentage, and octane
E85 is a fuel blend of up to 85% ethanol and at least 15% conventional petrol (gasoline). The "E" stands for ethanol; the "85" is the maximum E85 ethanol percentage. In practice, the actual blend varies by season: in cold climates the ethanol percentage in E85 may be reduced to as low as 51% in winter to ensure reliable cold-start performance — which is why the fuel is sometimes called "flex fuel" rather than strictly E85. What ethanol is E85? It is the same bio-based ethanol (bioethanol) used in E10 blends, derived from corn in the US or sugar cane in Brazil — just at a much higher concentration.
What does E85 mean? The name is simply a shorthand: E = ethanol, 85 = up to 85% by volume. What is E85 fuel? It is a high-ethanol petrol-type fuel for flex-fuel vehicles. Is E85 petrol or diesel? It is petrol (gasoline) — a spark-ignition fuel. It cannot be used in diesel engines. Is E85 alcohol? Yes, in the sense that ethanol (ethyl alcohol) is its primary component — but it also contains 15–49% conventional petrol, so it is not pure alcohol.
What is E85's octane rating? E85 has an octane rating of approximately 100–105 RON (or 94–96 AKI). Pure ethanol has a RON of about 109, so the high ethanol content of E85 gas gives it significantly better anti-knock performance than standard 95 RON petrol. This is why gasoline E85 is used in high-performance and motorsport engines — flex-fuel vehicles tuned for E85 can run higher compression ratios and advance ignition timing more aggressively than on regular petrol.
It is one point on a scale of ethanol blends: E10 and E15 are low-ethanol blends usable in ordinary petrol engines, while E85 sits at the high end and needs a compatible vehicle. Is E85 still a thing? Yes — it remains widely available in the US Midwest and Sweden, and is an established fuel grade in several other markets.
E10, E15 and E85 compared
Ethanol content is the main thing that separates these blends.
Which vehicles can use it
E85's high ethanol content means it isn't safe for every engine.
A standard petrol engine is not built for E85's higher ethanol content. Using it needs a flex-fuel vehicle (FFV), which can run on any blend from straight petrol up to E85.
Price per litre isn't the whole story
Ethanol holds less energy per litre than petrol, roughly a third less. E85 is usually cheaper per litre, but a car burns noticeably more of it to travel the same distance, so the fair comparison is cost per 100 km or per 100 miles, not price per litre.
The numbers below are illustrative, using a rough real-world consumption penalty for E85. Actual figures depend on the vehicle and current local prices.
Where E85 is sold
Where E85 is sold, and how easy it is to find, varies a great deal.
How this shows up on FuelTheGuide
E85 shows up as its own grade for the countries that publish it, rather than being folded into petrol or diesel. Most countries have no E85 data at all, and we show that as a dash, never as a zero.
If you want to compare running costs rather than pump prices, use the cost-per-tank and cost-per-distance figures in the explorer instead of the raw price, for the reason explained above.
See E85 in the fuel picker →Questions and answers
Does E85 damage a regular petrol engine?
It can. Ethanol is more corrosive to some fuel system materials and burns differently, so using E85 in a car that isn't flex-fuel rated risks damage and may affect the manufacturer's warranty.
Why is E85 usually cheaper per litre than petrol?
Ethanol is generally cheaper to produce than petrol, and in many markets it is subsidised to encourage its use as a biofuel. The lower energy content per litre means the pump price needs to be noticeably lower for E85 to be competitive on a per-kilometre basis.
Is E85 better or worse for the environment?
It depends on the feedstock and how it is produced. Sugar-cane ethanol, as used in Brazil, has a much lower lifecycle carbon footprint than petrol. Corn-based ethanol, common in the US, offers a smaller benefit. Land-use change, fertiliser and transport all affect the net figure. The US DOE Alternative Fuels Data Center summarises ethanol lifecycle emissions research.
How do I know if my car is flex-fuel?
Check the owner's manual or look for a badge near the fuel filler cap — flex-fuel vehicles often have a yellow cap or an FFV badge. In the US, the fuel door usually states the compatible fuel types. The US DOE maintains a list of flex-fuel vehicle models if you want to verify a specific make and year.
What is E85's octane rating?
E85 has an octane rating of approximately 100–105 RON (or about 94–96 AKI). Ethanol itself has a RON of around 109, so the E85 octane is far higher than regular 95 RON petrol. This is why E85 fuel is popular in tuned performance engines — engines optimised for E85 ethanol flex fuel can run significantly higher compression ratios than on standard petrol. The US DOE Alternative Fuels Data Center confirms E85 octane characteristics.
Is E85 petrol or diesel?
E85 fuel is petrol (gasoline), not diesel. It is a blend of up to 85% ethanol with at least 15% conventional petrol, used in spark-ignition engines — the same type that runs on regular petrol or gasoline. E85 is not diesel in any sense: it cannot be used in compression-ignition diesel engines and putting E85 in a diesel vehicle would cause serious damage. So to be clear: e85 fuel is petrol or diesel — it is petrol.
Is E85 still available, and what ethanol percentage does it contain?
Yes, E85 is still widely available in some markets. In the US it is sold at thousands of stations, particularly in the Corn Belt. Sweden has one of Europe's largest E85 networks. The E85 ethanol percentage typically ranges from 51–83% depending on season and region — the blend is adjusted in winter to improve cold-start performance, so what ethanol is E85 in winter may be closer to 51% rather than 85%. The bio ethanol E85 blend qualifies as a biofuel under most regulatory frameworks because ethanol is made from plant crops like corn or sugar cane.
E85 fuel compatibility and ethanol content in practice
E85 fuel compatibility is the single most important thing to check before filling up. Only flex-fuel vehicles (FFVs) — cars and trucks whose fuel systems, seals, and engine management are designed to handle up to 85% ethanol — can safely run on E85. Putting E85 into a standard petrol car risks damage to fuel lines, injectors and catalytic converters because ethanol is more corrosive and burns at a different air-fuel ratio than pure petrol. The U.S. EIA biofuels page explains the environmental trade-offs of ethanol blending, while the IEA biofuels tracking page monitors global ethanol production and blending mandates.
The actual E85 ethanol content is not always 85%. In cold climates, the blend is reduced to as low as 51% ethanol in winter to ensure reliable cold starts, because ethanol vaporises less readily than petrol at low temperatures. This seasonal variation means the fuel you pump in January may behave quite differently from the fuel you pump in July — affecting both performance and cost-per-kilometre. The UK government's fuels guidance covers fuel quality standards more broadly, and the European Commission's biofuels overview explains how ethanol mandates interact with EU climate targets.
More questions
Can any car run on E85, or does it need to be a flex-fuel vehicle?
No — only flex-fuel vehicles (FFVs) are designed for E85 fuel compatibility. Standard petrol engines use fuel system materials that can be damaged by the high E85 ethanol content (51-85% ethanol by volume). Using E85 in a non-FFV vehicle can corrode seals, swell rubber hoses and trigger engine management faults. Always check your owner's manual or look for an FFV badge before filling up with E85.
Sources and further reading
- E85 (flex fuel) US Department of Energy, Alternative Fuels Data Center, afdc.energy.gov
- Ethanol fuel blends US Environmental Protection Agency, epa.gov
- Fuel prices tool and grade lists OpenVan.camp, openvan.camp/compare/fuels/prices