Is gas bad after sitting for a year?

Quick Answer

Gas can go bad after sitting for as little as 3 to 6 months. The exact shelf life depends on the gas blend, additives used, and storage conditions. However, gas that has been stored properly in a sealed container for only a year will likely still burn fine in most engines. The main risks are decreased engine performance and extra build up in fuel lines or injectors.

How Long Can Gas Sit Before Going Bad?

Gasoline has a shelf life between 3 to 12 months before it starts to degrade in quality and burn less efficiently. The exact length of time depends on several factors:

Gas Blend

– Regular 87 octane gas lasts 3 to 6 months before going stale.
– Mid-grade 89 octane gas lasts 4 to 7 months before going stale.
– Premium 93 octane gas lasts 6 to 12 months due to having more detergents and stabilizers.

Higher octane gas has more additives that help it last longer in storage. However, even premium blends can start to go bad after about a year.


– Ethanol – Gasoline with ethanol (10% blend) breaks down faster, lasting 3 to 4 months before going stale.
– Stabilizers – Fuel stabilizers help gas resist breaking down for 12 to 24 months.
– Detergents – More detergents make gas last 6 to 12 months before going bad.

Gasoline with ethanol has a shorter shelf life. Using fuel stabilizers or buying brands with more detergents can extend how long gas lasts.

Storage Conditions

– Temperature – Gas lasts longer when stored at moderate temperatures between 40°F to 70°F. Heat and cold extremes speed up fuel degradation.
– Container – Gas lasts longer when stored in an airtight metal or HDPE plastic fuel container to prevent air exposure and evaporation.
– Volume – Tanks over 3/4 full have less air space and evaporation, allowing gas to last longer.

Proper storage at moderate temperatures in a sealed container allows gasoline to stay fresh for longer before going bad. Storing gas in partially filled containers, extreme temps, or porous containers causes it to go stale faster.

Does Gas Go Bad After a Year?

Gas that has been stored properly should still burn acceptably during the first year. However, gas over a year old risks the following issues:

Performance Problems

– Hard starting – Stale gasoline is less volatile and doesn’t vaporize as easily, causing hard starting.
– Poor driveability – Gasoline that has gone bad can cause sputtering, stalling, or loss of power while driving.
– Reduced mileage – As gasoline ages, it burns less efficiently, reducing fuel economy and gas mileage.
– Engine knocking – Older gas can cause premature combustion (detonation) leading to engine knocking or pinging.

Old gas has degraded combustion properties that affect engine performance, especially when accelerating or under load.

Fuel System Issues

– Gum and varnish – Oxidized compounds in bad gas leave sticky gum and varnish deposits that clog fuel lines, injectors, and carburetors.
– Corrosion – Stale gasoline creates acids that can corrode metallic fuel system components.
– Blocked filters – Contaminants from degraded gasoline plug fuel filters prematurely.

Gum, varnish, corrosion, and blocked filters are common fuel system problems from using old, spoiled gas that has been sitting too long.

Check Engine Light

The engine control module can detect performance issues caused by bad gasoline. This often triggers check engine lights for:

– P0301 – Misfiring cylinder
– P0302 – Ignition/fuel injection issues
– P0420 – Catalytic converter damage from engine misfires

Stale gas that causes engine misfires, ignition problems, or fouls the catalytic converter will turn on the check engine light.

Can Damaged Engines

In worst case scenarios, using very old gas that has degraded significantly can damage engines. Issues include:

– Burned valves and seats
– Stuck piston rings
– Clogged injectors
– Engine oil contamination

Highly degraded gasoline with oxidation products can damage internal engine components. However, gas that has been stored properly for only 1 year is unlikely to cause these issues.

How to Tell if Old Gas is Bad

Here are some signs that gas has gone bad while sitting in storage:


– Cloudy or dark – Gas turns from clear or light amber to an darker, opaque appearance.
– Particulates or water – Contaminants settle out or separate from bad gas.
– Slime or algae – Microbial growth in old gas produces slime, gel, or algae.

Cloudiness, particles, or slimy texture indicate microbial contamination and chemical changes in old gasoline.


– Sour or rotten eggs – Stale gas smells sour or like sulfur due to oxidation.
– Strong odor – Gasoline fumes become more pungent as lighter compounds evaporate.
– Gasoline odor disappears – Very old gas can lose its characteristic petrol smell as it breaks down.

A strong, sour, or missing gasoline odor can alert you to degradation in stored fuel.

Performance Testing

– Ignition test – Droplets of old gas may not ignite or combust poorly.
– Burn test – Bad gas burns weakly with yellow flames instead of a robust blue flame.
– Engine testing – Running an engine briefly on old gas can reveal performance issues.

Simple ignition tests by burning samples or running an engine can identify problems with stale fuel.

How to Revive Bad Gas That Has Been Sitting

Before using old gas that may have gone bad, try these tips to revive it:

1. Add Fuel Stabilizer

Fuel stabilizers contain antioxidants and biocides that help rejuvenate stale gasoline. They can extend the usability of gas sitting up to 2 years when added at recommended concentrations.

2. Add Fresh Gas

Mixing fresh and old gas 1:1 dilutes the degraded compounds and helps resolve performance issues in smaller engines. This works for gas sitting up to a year.

3. Add Octane Booster

Octane boosters revitalize old gas and restore lost volatility and combustibility. They treat common problems but can’t fix severely degraded gas.

4. Add Heet Fuel Additive

Heet contains iso-butanol to help dissolved water in bad gasoline for improved ignition and performance. It also has cleaning agents.

5. Drain and Refill

For gas over a year old, it’s often easiest and most effective to simply drain the old gas and refill with fresh gasoline. This avoids potentially expensive repairs.

6. Adjust Air-Fuel Ratio

Enriching the air-fuel mixture in the carburetor or computer helps compensate for lower volatility in old gas.

7. Change Fuel Filters

If degraded gas has contaminated or clogged the fuel filter, replacing it can resolve issues with fuel flow and pressure.

8. Clean Injectors

Fuel injector cleaning kits can remove gum, varnish, and other buildup caused by bad gas sitting for prolonged periods.

9. Drain Oil and Change Filter

Stale gasoline that has contaminated engine oil should be drained along with replacing the oil filter to clean the system.

Can You Store Gas Longer Than 1 Year?

Gasoline can be stored over 1 year without going bad by:

– Treating it – Fuel stabilizers allow gas to be stored 1-2 years. Biocides prevent microbial growth while antioxidants slow oxidation. Follow product instructions carefully.

– Storing underground – Keeping gas in underground tanks, well below the frost line, keeps it fresh for over a year since it stays cool and has less exposure to oxygen. Monitor tanks for water ingress.

– Adding preservatives – Strong preservatives like proprietary storage additives allow gas to stay fresh for 1-3 years by slowing degradation reactions. They maintain fuel volatility and combat oxidation and varnish.

– Nitrogen blanketing – Covering the gas with an inert nitrogen layer reduces oxidation, allowing gas to store longer term over a year without going bad.

– Freezing it – Gasoline frozen at 0°F in air-tight containers essentially stops aging reactions, allowing longer frozen storage over a year.

With proper fuel stabilizers, antioxidants, inert storage methods, or freezing, gasoline can often be stored for 18-24 months and remain usable.


While gasoline quality gradually declines after 3-6 months, gas that has been stored properly should be fine to use throughout the first year. The main risks when using gas over a year old are reduced performance, more buildup in the fuel system, and potential engine problems in worst case scenarios. However, there are many additives and treatments available to rejuvenate old gas and keep it burning properly in engines, even after storage longer than 12 months. With stabilizers and antioxidants, gas can even be stored 18-24 months before going bad.

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