ShelfYears

How long does gasoline last?

About 3–6 months in a sealed, approved can — Exxon's guidance is to use it within a month of purchase, and today's ethanol-blend pump gas sits at the short end of every window.

Updated

Gasoline
Sealed
3–6 months
Opened
1–3 months
OXIDATION
Equipment damage

Sealed: 3–6 months Tier 1

Exxon's storage guidance says gasoline should be used within a month of purchase, and that with good storage practice — a tightly sealed, approved can of five gallons or less, kept at room temperature away from heat — it remains good quality for six months, with a 6–12 month ceiling depending on the fuel type. Ethanol-blend pump gas ages fastest; treat six months as the honest end of the window.

After opening: 1–3 months Tier 1

A part-empty, repeatedly opened can ages faster than a sealed one: every opening admits fresh air and moisture, the light ends that carry cold-start performance evaporate, and the ethanol in E10 pulls water out of the air until the blend can separate.

How to tell it's gone off

  • Darker than fresh fuel — straw-coloured gas that has gone amber or brown is oxidized.
  • A sour, varnish-like smell from the can instead of the sharp ordinary gasoline smell.
  • Sticky gum or lacquer residue around the spout or cap threads.
  • A separate watery layer at the bottom of the can — an ethanol blend that has pulled in enough moisture to phase-separate.

If you use it anyway

Equipment damage

Stale gasoline is an equipment problem, not a you problem. As it oxidizes it forms gum and varnish that plug carburetor jets, injectors and fuel filters — STIHL calls improper fuel storage a leading cause of fuel system component failures, and the repair usually costs more than the fuel was worth.

Why it goes off — OXIDATION

Gasoline is a blend of light hydrocarbons that starts reacting with oxygen the day it leaves the refinery. Oxidation builds gum and varnish, the most volatile fractions evaporate first, and ethanol blends also absorb water — three clocks running at once, all of them faster in a warm shed.

Every page here commits to one of four states — Harmless · Degraded performance · Equipment damage · Safety issue. How the verdicts work.

How to store it

Exxon's rule set: an approved fuel can of five gallons or less, tightly capped, at room temperature, away from heat sources like sun, water heaters and furnaces, and ideally in a detached shed at least 50 feet from anything that makes a spark. Fuel stabilizer added to fresh gas extends the window; it cannot rescue gas that has already gone off.

Do not pour old gasoline down a drain.

Sources