Is your petrol really E20? Here’s how you can check its ethanol content at home

E20 petrol has become a talking point among motorists across India as ethanol blending in petrol reaches the 20 per cent level. Average ethanol blending reached 20 per cent during the 2025-26 Ethanol Supply Year, according to the Centre. The government has also said that no decision has been taken to increase the nationwide blending level beyond 20 per cent at present.

While E20 has been at the centre of discussions over vehicle compatibility and fuel quality, there are also claims that petrol may sometimes contain more than 20 per cent ethanol. These remain claims and cannot be treated as established fact without proper testing.

If you are curious about the ethanol content of the petrol you have purchased, there is a simple water-separation method that can give you an indication. The principle behind it is straightforward. Ethanol mixes more readily with water than petrol does. When water is added to ethanol-blended petrol and the mixture is shaken, some of the ethanol moves into the water. Once the mixture settles, the water and extracted ethanol form the lower layer while petrol remains above it.

A water-extraction procedure based on this principle is also documented by IndianOil for testing ethanol-blended Motor Gasoline.

What you need

• A transparent graduated measuring cylinder or similar container
• 100 ml of petrol
• 30 ml of clean water

IndianOil's documented procedure uses a graduated, stoppered glass cylinder and specifies precisely 30 ml of water for a 100 ml fuel sample.

How to do the test

• First, measure 100 ml of petrol and pour it into the graduated container.
• Add 30 ml of water to the petrol and close the container securely.
• Shake the container vigorously for at least 30 seconds. The IndianOil procedure then calls for briefly loosening the stopper to release vapour pressure before tightening it again.
• Place the container upright on a level surface and leave it undisturbed for at least five minutes.
• As the mixture settles, two layers should become visible. The petrol will form the upper layer, while the water and ethanol extracted from the petrol will settle at the bottom.
• Now check the volume of the lower layer.

What does the reading tell you?

The test starts with 30 ml of water. Therefore, any increase in the volume of the lower aqueous layer represents ethanol that has moved into the water.

For example, if the lower layer measures 50 ml after separation, the increase over the original 30 ml is 20 ml.

However, this figure should not simply be treated as an exact ethanol percentage. IndianOil's formal procedure uses a standard calibration plot prepared with samples containing known ethanol concentrations to determine the corresponding ethanol content.

In other words, the water-separation test can provide an indication of the ethanol content, but it is not an authoritative laboratory measurement. If the exact composition of the fuel needs to be established, a proper laboratory test is required.

Don't forget the safety aspect

• Petrol is highly flammable, so this is not an experiment to be carried out casually.
• Keep the fuel well away from flames, cigarettes, sparks, running engines and other sources of ignition. Work only in a properly ventilated area and use a suitable container. The sample should also be handled carefully and kept away from children.
• The water-separation method can offer motorists a way to understand the basic ethanol-separation principle and get an indication from a fuel sample. But if there is a serious concern about the quality or composition of petrol purchased from a pump, professional fuel testing remains the reliable way to establish the actual ethanol content.