Red gasoline cans and a yellow diesel can on a detached shed shelf next to a portable generator

01Power & Backup

Storing Gasoline and Diesel: How Long It Lasts

How long stored gas and diesel stay usable, what stabilizer adds, how ethanol changes things, and how to store and rotate fuel cans safely.

Read: 8 min
Updated: October 6, 2026

Plain gasoline (E10 from the pump) starts to go stale in about a month and should be used within about 3 months. Add a storage stabilizer the day you buy it and it can stay usable for up to 2 years, according to the maker of STA-BIL. Diesel holds up longer. Untreated, it's good for roughly 6 to 12 months. With a stabilizer and a biocide it can last 12 to 24 months. In both cases, how you store it matters as much as what you add to it.

Almost everyone needs this in the fall. The generator gets pulled out, you fill a few cans, and those cans sit until the first ice storm. Here's how to keep that fuel good enough to start an engine when you need it.

01Why gasoline goes bad

Gas is a blend. The lightest parts evaporate first, and those are what make a cold engine start easily. A Department of Energy study found that gasoline gets stale before ethanol's water absorption becomes a problem, and that in hot, humid storage it weathered a lot within about one month.

As gas oxidizes, it leaves gum and varnish behind. In a small engine that means a clogged carburetor jet, which is why a generator that ran fine in March surges or won't start in November.

You'll see it and smell it. Fresh gas is clear to pale. Old gas turns darker, smells sour like varnish, and can leave a sticky film on a dipstick or a rag.

02What ethanol changes

Most pump gas in the U.S. is E10, meaning up to 10% ethanol. Ethanol pulls in water. Once enough water gets in (industry sources put it around 0.5% by volume), the water and ethanol drop out together and settle to the bottom of the can or tank. That's called phase separation.

The bottom layer is what a generator's fuel line draws first, and an engine won't run on it. Mixing doesn't fix it, because the gas left on top has lost its ethanol and some of its octane.

A rule of thumb you'll hear is 90 days for E10 before separation is a risk. In practice it often takes longer, and the gas usually goes stale first. Still, plan on 3 months as the limit for untreated E10.

Ethanol-free gas (sold as "rec fuel" or "marine gas" at some stations) stores better and is easier on small engines. It costs more per gallon and you won't find it everywhere. If a station near you sells it, use it for the generator.

03Stabilizer: what it does and doesn't do

Stabilizer slows oxidation. It can't bring stale gas back. Add it when the fuel is fresh, ideally right at the pump.

STA-BIL Storage, the most common brand, calls for 1 ounce per 2.5 gallons, so a 5-gallon can takes 2 ounces and a 16-ounce bottle treats 40 gallons. The maker says it keeps gas fresh for up to 24 months and works with ethanol and non-ethanol fuel. After you treat the fuel, run the engine about 5 minutes so treated gas fills the carburetor and lines. The bottle has its own shelf life too: 2 years after opening, or 5 years from the production date.

Treat "up to 24 months" as the best case. A sealed can kept in a cool shed will reach it. A vented can on a sunny porch won't.

04Why diesel lasts longer, and what kills it

Diesel doesn't have gasoline's light ends to lose, so it stays usable longer. Untreated diesel is typically good for 6 to 12 months, and it starts slowly breaking down within the first month even in a clean, sealed container.

Its main enemy is microbes. Bacteria and fungus grow where water meets fuel at the bottom of a tank. Today's ultra-low-sulfur diesel is more prone to this than the old high-sulfur fuel. You'll know it's happening when you see dark slime, a cloudy layer at the bottom, or filters that keep plugging.

For storage longer than a few months, treat diesel with a stabilizer (slows oxidation) and a biocide (kills the growth). Fuel suppliers recommend re-dosing the biocide about every 6 months if the fuel sits a long time. Treated diesel kept near 70°F can last 18 to 24 months.

05Containers and where they go

Use cans built for fuel and labeled to a standard (DOT, ASTM, UL or NFPA 30). Milk jugs, glass jars and old bleach bottles don't count.

The colors aren't decoration. Red is gasoline, yellow is diesel, blue is kerosene. If you run a gas generator and a diesel tractor, buy the matching colors so nobody grabs the wrong can at 2 a.m. by headlamp.

Where the cans live:

Detached shed or garage is best.
Attached garage works for a small amount, away from the water heater, furnace, dryer or anything with a pilot light or a spark.
Never in the basement or the house. Gas vapor is heavier than air and settles low, right where pilot lights are.
Not in the car. Take the cans out of the trunk or truck bed once you're home.
Out of direct sun. Heat speeds up aging and makes cans swell and vent.

06How much you're allowed to store

This depends on where you live. Fire codes are adopted and amended locally, so the limit in one town can differ from the next town over.

For a sense of typical numbers, Lehi, Utah's fire department sets these residential limits:

Gasoline: 25 gallons total, no more than 10 gallons in an attached garage, none in a basement, and no single can over 5 gallons.
Diesel and kerosene: 60 gallons total, no more than 25 gallons in an attached garage, none in a basement.
Empty cans count as full when you add up your total.
Store more than 5 gallons of gas and you need a 2A10BC fire extinguisher mounted 10 to 50 feet away.

Many towns use limits close to these, but plenty don't. Your HOA, lease or homeowner's policy may be stricter too. Check your local fire department's rules before you build a 20-can stockpile.

07Filling cans the safe way

Most gas can fires start at the pump or in the garage, not in storage. The National Park Service's fire guidance and fuel-safety sources agree on these steps:

Set the can on the ground to fill it. Never fill it in the truck bed or trunk. A plastic bed liner insulates the can, static builds up, and a spark can light the vapor.
Keep the nozzle touching the can's opening while you pump so static drains off.
Fill only to about 95%. Gas expands as it warms, so leave some air space.
Fill by hand. Don't use the nozzle's hold-open latch on a can.
Wipe the can off before it goes in the vehicle, and cap it tight.

08A rotation system that works

Stored fuel only helps if it's still good when the power goes out. The easiest way is to use it and replace it on a schedule.

Label every can with the fuel, date bought and "stabilized Y/N." Masking tape and a marker work fine.
Gasoline: for untreated E10, pour the oldest can into your car within about 3 months. For stabilized gas, rotate at least once a year. Fall is a good time, since you're starting the generator in October anyway.
Diesel: rotate yearly into a truck or tractor, or re-dose the biocide every 6 months if it's sitting longer.
Mix old into a full tank, not an empty one. A few gallons of slightly aged gas in a mostly full car tank gets diluted. Don't put questionable gas in a small engine.
Bad fuel goes to household hazardous waste. Dark, layered, slimy or sour-smelling fuel gets dropped off at your county's collection program. Don't pour it on the ground or into a drain.

09How much to keep on hand

That depends on what you run and for how long. A portable generator running a fridge, furnace blower and some lights can burn through a 5-gallon can in under a day. We do that math in Generator Fuel: How Much for a Day. Size the stockpile to your generator and your local storage limit, then rotate it so it never gets older than you planned.

If the storage limits or the rotation are more hassle than you want, a portable power station needs no fuel at all and can handle the small loads.

10This week's checklist

Count your cans, including empty ones, and compare the total to your local limit.
Date-label every can.
Add stabilizer to any gas you plan to keep past a month, then run the generator 5 minutes.
Move any cans that are in the basement, the car or next to the water heater.
Put a 2A10BC extinguisher where the code says it goes.
Read Generator Safety: Carbon Monoxide, Placement, and Backfeeding before the first outage, not during it.

Sources (6)