---
title: "Does Petrol and diesel expire? Degrades in quality"
description: "Petrol goes stale within months, and ethanol blends go faster because they absorb water. What actually changes over time, whether it matters, and how to store it."
url: https://atoneplace.net/does-it-expire/petrol/
site: "At One Place"
---

# Does Petrol and diesel expire?

**Does Petrol and diesel expire?: Petrol goes stale within months, and ethanol blends go faster because they absorb water.**

Petrol: 3-6 months. E10: closer to 3. Diesel: 6-12 months. With stabiliser: 1-2 years

Petrol loses its lighter, more volatile fractions to evaporation, which is what makes an engine hard to start on old fuel. Ethanol-blended petrol has a second problem: ethanol is hygroscopic and pulls water out of the air, and past a certain point the water and ethanol separate out as a layer at the bottom of the tank that an engine cannot run on. This is why small engines — mowers, generators, outboards, motorcycles left over winter — suffer far more than cars, which cycle their fuel constantly. Diesel keeps longer but grows a microbial sludge at the fuel–water interface if it sits.

## How to store it

- Fill the tank before storing something over winter — a full tank has less air, so less condensation.
- Fuel stabiliser genuinely works, and is far cheaper than a carburettor rebuild.

## How to tell it has gone

- A varnish-like or sour smell instead of the sharp normal one.
- Darkened colour, or a visible separated layer in a clear container.

> "Use by" and "best before" are legally different. Use-by is a safety date and should be respected; best-before is about quality, and food is usually fine well past it. Where the two diverge matters, the page above says which applies.

## Common questions

### Does Petrol and diesel expire?

Petrol goes stale within months, and ethanol blends go faster because they absorb water.

### How long does Petrol and diesel last?

Petrol: 3-6 months. E10: closer to 3. Diesel: 6-12 months. With stabiliser: 1-2 years

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## Sources

- US Environmental Protection Agency — EPA (https://www.epa.gov/) [Public domain (US Government)]