Does Gas Go Bad? How Long It Lasts and What to Do With Old Gas

Published Oct 23, 2026 · 6 min read · By Hassan, Owner of Roadmate Services

Does gas go bad? Yes. Regular gas lasts about three to six months before it starts to lose quality, according to J.D. Power and AAA Club Alliance. It has no printed expiry date, but it does expire in practice: it slowly gets harder to burn and can leave your car hard to start.

Gas looks the same on day one and day 180. Your engine can tell the difference.

Quick answer: how long does gas last?

Published market figures from named sources, for fuel kept sealed and out of the heat.

Sources: J.D. Power, AAA Club Alliance, Bob Vila. Checked October 2026.

Why no separate ethanol row? Most gas sold in the US is already about 10% ethanol (E10), according to the U.S. Energy Information Administration, so the regular-gas range already covers it.

Fuel is one of the few things that gets worse while you save it for later.

Will gas go bad in your car’s tank?

Yes, on the same three-to-six-month clock. And the clock starts before you park: J.D. Power notes that gas can already be over a month old when it comes out of the pump.

J.D. Power says a full tank keeps air and water out, while an emptier tank is more prone to rust. Stored in a can instead? See how long gas lasts in a gas can.

A car parked for the winter is on vacation. The gas inside it is still clocking in.

Why gas goes bad

• Oxidation: air reacts with the fuel, and it burns less well.
• Evaporation: the lighter parts of gas evaporate first, so old gas is harder to ignite.
• Ethanol and water: ethanol attracts moisture. Enough of it, and the gas and ethanol separate into layers.

None of this happens overnight. It is more like a bag of chips left open: not dangerous, just slowly less useful.

How to tell if gas has gone bad

Pour a little into a clear glass jar outdoors and compare it with fresh gas. Signs of bad gas:

• It is darker than fresh gas.
• It smells sour or unfamiliar.
• There is sediment or debris in it, or separate layers.

Per Bob Vila, slightly sour or slightly darker usually means old but usable. Strong discoloration, sludge or layers mean contaminated. Keep the sniff short; gasoline fumes are not something to breathe in.

What old gas does to your car

AAA Club Alliance lists the usual symptoms of bad fuel:

• Hard starting
• Rough idling, pinging or knocking
• Stalling
• A check engine light
• Worse fuel economy

Badly degraded or watery gas needs the tank drained and the fuel system checked. That is a shop job, not a roadside one, and we will say so rather than sell you a visit that will not fix it.

A lawn mower that coughs all spring is not being lazy. It is filing a complaint about the fuel.

Car sat for months and will not start?

Check the battery first. Clicking or a slow crank points to the battery, not the fuel. Our guide on what to do with a dead car battery covers the options.

In Columbus, we can jump it, then test the battery, the alternator and the charging system. If the battery is bad, we offer a replacement on site. If the engine cranks strongly but will not run right on old fuel, it needs a mechanic, and we can tow it to the shop in Columbus.

Cars that sit for months rarely have only one problem. Boredom is contagious under the hood.

What to do with old gas

Small amount, slightly old, still clear

You can usually mix it with fresh gas. Bob Vila suggests no more than one part old gas to one part fresh, and warns the engine may still sputter. Check your owner’s manual first.

If the car starts and runs fine, you do not need us or a shop. Fill up and drive it.

Old, dark or contaminated: do not use it

Gas that is dark, sludgy, layered or has water in it goes to hazardous waste, not into an engine. Old gas is one leftover that no amount of creative reheating will save.

How to dispose of old gas safely

Gasoline is household hazardous waste. Here is how to get rid of old gas in Columbus, based on the City of Columbus and SWACO. Our technicians do not take away old or contaminated gas, so a drop-off is the place for it:

1. Never pour gas down a drain or sewer, on the ground, or into the trash, and never burn it.
2. Keep it in an approved, sealed gas can. Do not pour it into milk jugs or bottles to carry it.
3. Carry it upright and secured, away from the passenger area, such as in the trunk or a pickup bed, as Mass.gov advises. Drive straight there.
4. Take it to the SWACO household hazardous waste drop-off at 645 E. 8th Avenue, Columbus. It serves Franklin County residents and accepts old gasoline and gas mixed with oil. SWACO lists weekday hours plus the first Saturday of each month (checked October 2026); check its page or call before you go.
5. Outside Franklin County, ask your city waste office or fire department for the nearest approved drop-off.

How to keep gas from going bad

1. Storing a car? Fill the tank with fresh gas first. A full tank leaves less room for air and moisture.
2. Add fuel stabilizer to fresh gas and follow the label. It will not rescue gas that has already turned.
3. Start the car and run it for 10 to 15 minutes each week if it sits a lot, as AAA Club Alliance suggests.

A full tank and a bottle of stabilizer are cheap compared with a mechanic calling to say they found the problem.

Frequently asked questions

The bottom line

Gas does go bad: regular gas in about three to six months, diesel in up to a year. Slightly old gas can be mixed with fresh; dark or contaminated gas goes to a hazardous waste drop-off. A car that sat for months and will not start needs the battery checked first.

As Hassan puts it: “Most fuel calls happen on the highway, when the driver has not paid attention to the gas gauge. Please look at it.” Fresh gas only helps if there is some in the tank.

May your next fill-up be the most uneventful thing you do all week.