Does E20 petrol reduce mileage?
Short answer: official testing says a modest change - surveys sometimes report more. Ethanol has a lower energy content than petrol, so E20 can reduce fuel economy. The debate in India is about how much: official testing is typically cited around 1-6% (sometimes 2-6%), while some owner surveys self-report larger drops in real driving. Those surveys are not ARAI lab results.
Read both carefully: ARAI / govt-cited testing is about ~1-6%. A June 2026 LocalCircles survey of responding pre-2023 petrol owners found 66% self-reporting a mileage drop of over 10%. Survey responses are voluntary and unverified.
Why ethanol lowers mileage
Ethanol contains roughly a third less energy per litre than petrol. A 20% blend therefore carries slightly less energy overall, so your engine needs a bit more fuel to do the same work. The theoretical energy difference for E20 is around 3-4% - but real-world results vary a lot by vehicle, age and how it's tuned.
What the official numbers say (ARAI)
The Automotive Research Association of India (ARAI), which tested vehicles for the government, reported a fuel-economy reduction of about 2-6% on E20 compared with E10, depending on the vehicle. It said drivability, startability and acceleration were unaffected in compatible vehicles. The Ministry of Petroleum & Natural Gas later acknowledged a 3-5% drop "in some vehicles."
What some owner surveys report
Owner surveys can show larger self-reported drops than lab figures. In the LocalCircles June 2026 survey, 66% of responding pre-2023 petrol owners self-reported a >10% mileage drop (up from 45% a month earlier in that survey). That is survey data - not an official MoPNG/ARAI fleet finding.
Both can be true in different contexts: lab-tested compatible vehicles often show a modest change; older vehicles and different driving conditions can produce different owner-reported results. Larger self-reported drops are not verified by ARAI as a fleet-wide finding.
Why your mileage might drop more than 6%
- Your vehicle was tuned for E10/E5, not E20.
- Older engines, injectors and filters aren't optimised for the blend.
- Driving conditions - city traffic, AC, load, tyre pressure - amplify any difference.
- The pump price didn't fall to offset the energy difference, so the cost feels worse.
How to measure your real E20 mileage
- Fill the tank completely and note the odometer.
- Drive normally until you refuel, then fill completely again.
- Divide km driven by litres added - that's your true km/l.
- Repeat 2-3 times and average for accuracy.
Want the rupee impact instead? Our Mileage & Cost Calculator turns any mileage drop into extra spend per month, year and over five years.
Sources
ARAI / SIAM / IOCL testing (government-cited); Ministry of Petroleum & Natural Gas FAQ, July 2026; LocalCircles surveys (May-June 2026); BBC, Economic Times and Times of India reporting, 2026. Figures are as reported publicly and may be updated as more data is released.