Yes, car mileage with ethanol-blended fuel is a bit lower, but only marginally so. Since ethanol has about one-third less energy per litre than petrol, the energy release would be slightly less if you burn fuel that contains ethanol. A regular petrol car is estimated to see mileage drop by 1% to 3% on E10 (fuel mixed with 10% ethanol) and by 3% to 6% on E20 (fuel mixed with 20% ethanol), depending on the engine type and driving style.
Ethanol is a plant-based alcohol produced in India mainly from sugarcane and grain, and when mixed with petrol, it helps reduce crude oil imports and vehicle emissions. The number in the name indicates the blend: 10% ethanol and 90% petrol in E10, versus 20% ethanol and 80% petrol in E20.
Why does ethanol lower car mileage at all?
Since ethanol has less energy per litre compared to petrol, your mileage will decrease. Your engine doesn't know the difference between litres and energy; it's the energy that powers it, and so a fuel delivering less energy per litre will require you to get an extra bit of fuel for covering the same distance.
Roughly 32-34 megajoules of energy are contained in a litre of petrol, whereas ethanol only gets about 21 megajoules almost as much as losing a third of your energy source. The mixture's overall energy content will drop by the same percentage if ethanol is added.
| Fuel type | Ethanol share | Approx. energy per litre |
|---|---|---|
| Pure petrol (E0) | 0% | ~33 MJ |
| E10 | 10% | ~32 MJ |
| E20 | 20% | ~31 MJ |
| Pure ethanol (E100) | 100% | ~21 MJ |
E10 reduces energy content by only 2% to 3%, so the mileage loss is still in the low single digits. E20 almost doubles that reduction, but modern engines compensate somewhat for the difference as ethanol has a higher octane rating and can be burned more efficiently. Hence, the actual loss is often lower than the difference in raw energy would indicate.
How much does car mileage actually drop on E10 and E20?
Cars not adapted for ethanol will usually experience a drop in the fuel range of about 1% -3% on E10 and about 3% -6% on E20 fuel consumption for a regular petrol engine, cars designed or calibrated as "E20-ready" usually consume the lowest fuel range of E20 because engines are made to be compatible with this fuel blend.
| Blend | Ethanol content | Typical mileage change (non-optimised car) | Typical mileage change (E20-ready car) |
|---|---|---|---|
| E0 (pure petrol) | 0% | Baseline | Baseline |
| E10 | 10% | 1% to 3% lower | Around 1% lower |
| E20 | 20% | 3% to 6% lower | 2% to 4% lower |
These are just rough ranges. The actual amount will be affected by your engine design, its age, whether it has been well cared for, and also your driving style.
A driver who seldom stops may not be aware of it at all; however, a vehicle being held up in thick city traffic will definitely notice a decline in performance.
What does the car mileage drop cost you in rupees?
Rupee impact changes a little, which you might not expect. An example is provided so you can see the actual money involved, rather than just a percentage.
Car A: 18 km per litre with pure petrol, driven a yearly mileage of 12,000 km, petrol rate is Rs 100 per litre.
| Scenario | Effective mileage | Litres for 12,000 km | Annual fuel cost |
|---|---|---|---|
| Pure petrol (E0) | 18.0 km/l | 667 litres | Rs 66,700 |
| E10 (2% drop) | 17.6 km/l | 682 litres | Rs 68,200 |
| E20 (5% drop) | 17.1 km/l | 702 litres | Rs 70,200 |
Based on these calculations, E10 fuel would cost you approximately Rs 1,500 extra annually and E20 around Rs 3,500 extra a year in fuel alone, prior to considering differences in pump prices. Since ethanol blends are usually priced similarly to, if not a bit less than, pure petrol at the pump, the real cost difference for you could very well be much less than what this chart indicates, and it may even be practically zero!
Is E20 safe for your car, and is it mandatory?
E20 is safe to use in most modern petrol cars. India is moving towards it as the standard blend. Through the Ethanol Blended Petrol scheme, at the national level, India achieved 20% ethanol blending, much ahead of its target year of 2025-26, meaning E20, that is, fuel containing 20% ethanol, became the default fuel.
If you have an old car and are worried about ethanol-related wear and tear on the fuel system, it might be worthwhile to check whether your car insurance covers engine damage as part of the policy.
Car manufacturers are promoting new cars as "already equipped for E20": they have confirmed that these vehicles can handle up to 20% ethanol-blended fuel without any issues. Starting around 2023, several car makers have released models that can run on E20 fuel.
Old "E10-compliant" vehicles: They can run on E20 fuel and won't necessarily cause any short-term mechanical problems. However, E20 has a higher ethanol content. With longer use, this might be more corrosive to certain ageing components of the fuel system (like rubber seals, gaskets, etc.) and could also decrease fuel efficiency slightly more than an updated engine.
Powder-old or naturally aspirated engines: These are the ones that really should be inspected thoroughly because ethanol is a good solvent that can attract moisture from the air, thereby degrading both rubber and metal components. If the rubber already has some weathering, this effect would be more pronounced.
If you are not sure what blend is recommended, it would be wise to check the car's owner's manual or refer to the fuel-cap area for the specified blend of your car. It is quite an essential step to get the right blend of fuel because not only will it be good for mileage, but it will also protect the engine from getting damaged.
If you are concerned about engine or fuel system damage from ethanol use, read our detailed guide on car insurance cover for E20 fuel engine damage to understand what your policy does and does not cover.
Small habits recover most of the loss
A difference in mileage between 1% and 6% that results from using ethanol could be less significant than the negative effect caused by poor maintenance practices. It is possible to save several percentage points of fuel efficiency by maintaining proper tire pressure, scheduling timely service, carrying less unnecessary load, and accelerating smoothly.
Are there any upsides to ethanol blending?
Yes. There are a number of benefits that come with the small sacrifice of mileage that make India implement the program.
Less pollution: Ethanol produces less pollution by reducing carbon monoxide emissions compared to conventional gasoline alone.
Less oil importation: When ethanol is blended into the country's fuel, it reduces the quantity of crude oil imported.
Boosts farming: Ethanol can be derived from grains and sugar cane, providing an outlet for farm produce.
Increase in octane level: Ethanol raises the fuel's octane level.
Key Takeaways
While the consumption of ethanol-blended petrol increases, it does so only marginally because ethanol has one-third less energy per litre than petrol.
The increase in consumption is a little bit higher if the engine hasn't been designed to handle a higher level of ethanol in the fuel, for instance, consumption can go up by around 1% to 3% if a normal petrol engine is run on E10 (10% ethanol) and 3% to 6% when the same engine is run on E20 (20% ethanol).
If the cars are 'ready for E20', there will be minimal reduction in mileage since the engines are tuned for the blend.
To illustrate in a numerical example, (consumption of 18 km/l, 12,000 km per year, price of petrol is Rs 100/litre), E10 adds Rs 1,500 to Rs 3,500 to the cost of fuel annually before the pump-price effect.
In India, the country achieved an average ethanol blending level of 20% much earlier than the deadline set for 2025-26; hence, E20 is now the default fuel.
The ethanol blend helps reduce tailpipe emissions, reduce crude oil imports, and benefit the domestic agricultural sector.
Frequently asked questions
In general, using E20 fuel will not harm vehicles designed to use E10 fuel. The risk that older engines face comes from prolonged use of E20 fuel, since the increased ethanol content may be corrosive to ageing rubber components and can absorb water.
About the authors
Nikhila PS
Written by · Senior Content EditorNikhila is a content creator with 6+ years in EdTech and motor insurance, turning complex policies into clear, engaging content. She enjoys exploring digital trends, social media, and art while planning her next short escape.
Rekhit Singh Kaushal
Reviewed by · Senior Director - Motor UnderwritingRekhit Singh Kaushal is Senior Director at ACKO, a leading digital motor insurance provider in India. With deep expertise in insurance strategy and innovation, he brings trusted insights on car and bike insurance to help drivers stay protected.
