Three credible sources give three different numbers for how long gasoline keeps. Chevron says a tightly closed container in a cool place holds its quality for at least a year. ExxonMobil says use it within a month, or six to twelve months if stored properly. Briggs & Stratton says thirty days. None of them is wrong. They are answering different questions, and once you see which question each one answers, you know how to store fuel so it lasts.
The short answer
Gasoline in a sealed container, filled to about 95 percent, kept cool and out of direct sun: plan on a year, and rotate it before then. Gasoline in a vented engine tank or a container that breathes: a month or two before it starts causing trouble in small engines. Gasoline in a hot shed or a truck bed in summer: add a stabilizer at fill time or plan on using it quickly. Everything below is the reasoning behind those three sentences, with the sources named.
What happens to gasoline as it sits
Gasoline is a blend of a few hundred hydrocarbons plus additives, and it degrades by three separate mechanisms. Each one is affected by different things, which is why storage advice sounds contradictory until you separate them.
Oxidation: gums and peroxides
Gasoline reacts with oxygen. Chevron's motor gasoline technical review describes the chemistry from the additive side: oxidation inhibitors "prevent gasoline components from reacting with oxygen in the air to form peroxides or gums," and are "needed in virtually all gasolines but especially in those with high olefin content." The consequences are specific: "Peroxides can degrade antiknock quality, cause fuel pump wear, and attack plastic or elastomeric fuel system parts. Soluble gums can lead to engine deposits, and insoluble gums can plug fuel filters" (Chevron). Every gallon at the pump already contains antioxidant; the gasoline specification, ASTM D4814, includes an oxidation stability requirement "to protect against the formation of additional gum by air oxidation during storage" (Chevron). Oxidation runs faster at higher temperatures and with more air contact. It runs slower cold, sealed, and with a stabilizer, which is simply more antioxidant.
Evaporation: losing the light ends
The components that make gasoline easy to start in cold weather are also the most volatile. In a container that breathes, through a vent, a loose cap, or a wall that lets vapor through, they leave first. The fuel that remains is harder to ignite and has a different distillation curve than what the engine was tuned for. This is the loss a properly sealed can prevents almost entirely, and it is the reason a can that holds vapor pressure matters more than most people think. Chevron's advice to leave the container 95 percent full is about the flip side of the same property: warm gasoline expands and generates vapor, and "without space to expand, the vaporizing gasoline will create pressure that will distort the container and even force liquid gasoline out of it" (Chevron).
Water and ethanol: phase separation
Most US gasoline is E10, ten percent ethanol. Ethanol dissolves in water and gasoline does not, and that changes how stored fuel behaves. Conventional gasoline can hold roughly 150 parts per million of water at 70°F; E10 can hold 6,000 to 7,000 ppm (Chevron). The EPA puts the E10 limit at 60°F at about 0.5 percent by volume, "approximately 3.8 teaspoons of water per gallon of the fuel before the water will begin to phase separate" (EPA). Past that point, or when the fuel cools, the water drops out and takes the ethanol with it. Chevron describes the result: "two layers of liquid: an upper ethanol-deficient gasoline layer and a lower ethanol-rich water layer," and "after phase separation, the gasoline layer will have a lower octane number and may cause knocking. The fuel also is less volatile. An engine will not run on the water-ethanol layer" (Chevron). Water gets into stored fuel from humid air pulled in through a vent or a poor seal as the can cools each night. A sealed container with minimal headspace has very little air to pull moisture from.
The numbers, and who says them
| Source | What it says | What it is really describing |
|---|---|---|
| Chevron, Motor Gasolines Technical Review | "Gasoline stored in a tightly closed container in a cool place will retain its quality for at least one year." | Best-case container storage: sealed, cool, 95% full. |
| ExxonMobil, gasoline storage guidance | "In general, gasoline should be used within a month of purchase." With proper storage, "between six and 12 months, depending on the fuel type." | A conservative default, plus a realistic range for approved containers stored properly. |
| Briggs & Stratton, equipment storage | "Gas begins to degrade in as little as 30 days." | Fuel left in a vented small-engine tank and carburetor, where deposits form in tiny passages. |
Read together, the picture is consistent. The engine maker is warning about fuel in the machine, where it sits in a vented tank and a carburetor bowl that gums up with a few milligrams of deposit. The refiners are describing fuel in a closed container. The difference between one month and one year is mostly the container and the temperature, which are the two things you control.
How to store gasoline so it lasts
- Use a container that actually seals. This is the single largest variable. A cap that compresses a gasket and locks, on a body that does not distort in heat, keeps the light ends in and the moisture out. It is the reason the NATO jerry can was designed with a cam-lever closure rather than a screw cap in the first place; see What Is a NATO Jerry Can? for how that closure works.
- Fill to the line, not the brim. Chevron's 95 percent rule leaves room for expansion. On a Wavian can the fill line leaves the air pocket under the handles, which is where the breather pipe ends. Less headspace also means less oxygen and less moist air in the can.
- Keep it cool and shaded. Chevron's threshold is explicit: if the container "will be in direct sun or will be heated above 30°C (80°F) much of the time, add an aftermarket fuel stabilizer when you fill it with gasoline" (Chevron). ExxonMobil says to store fuel "at room temperature, away from potential heat sources such as the sun, hot water heaters, space heaters or furnaces" (ExxonMobil). A north wall of a detached shed beats a south-facing truck bed by a wide margin.
- Add stabilizer at fill time if the fuel will sit. Stabilizer is antioxidant. It slows gum formation in fuel that is still good; it does not repair fuel that has already oxidized. Use the treat rate on the product and add it before the fuel goes into the can so it mixes.
- Label and date the can. Write the fuel type and the fill month on tape or a label. Color helps, red for gasoline, yellow for diesel, but a date is what tells you when to rotate.
- Rotate on a schedule. The simplest system is to pour stored fuel into a vehicle every few months and refill the can with fresh. A vehicle's fuel injection is far more tolerant of slightly aged fuel than a generator or mower carburetor. For equipment going into storage, ExxonMobil's advice is to "drain the fuel tank and then run the engine until it stalls" (ExxonMobil).
Where you are allowed to store it
This is where the rules become local, and where a lot of internet advice is simply wrong. There is no single national limit on gasoline at home. Here is what the actual documents say.
- Model fire code. The International Fire Code, which most US jurisdictions adopt with amendments, states: "Quantities not exceeding 10 gallons (38 L) are allowed to be stored outside of a cabinet when in approved containers located in private garages or other approved locations" (IFC 2021 §5704.3.4.4). Above 10 gallons the code expects a flammable-liquid storage cabinet. How those limits play out for a generator reserve, a ranch, or a vehicle is in Fuel Storage for Off-Grid, Ranch, and Overland Use.
- Local amendments vary widely. Syracuse, Utah caps residential flammable liquids at 30 gallons, "preferably stored in an unattached garage or shed" (City of Syracuse). Bluffdale, Utah, one county over, recommends no more than 5 gallons (City of Bluffdale). Your fire marshal's office will tell you your number in one phone call.
- Workplace reference point. OSHA's construction standard: "No more than 25 gallons of flammable liquids shall be stored in a room outside of an approved storage cabinet" (29 CFR 1926.152(a)(2)). That rule governs job sites, not homes, but it is the number many local codes borrowed from.
- Placement. ExxonMobil: "Store fuel in a detached shed or garage, at least 50 feet away from ignition sources, such as pilot lights. Fuel vapors are heavier than air and can travel along the floor to ignition sources" (ExxonMobil). The US Fire Administration: "Store anything that can catch on fire away from your home" and "Never store materials that can cause a fire in the sun or near an open flame or heat source" (USFA).
Two practical notes. First, vapor is the mechanism behind most of these rules; every one of them is about keeping fuel and its vapor away from living space and ignition sources. Second, a can in a holder cannot tip, slide, or get knocked over by a lawnmower, which is how most garage spills happen.
Diesel is different
Diesel does not evaporate light ends the way gasoline does, and it is not blended with ethanol, so two of the three gasoline problems mostly disappear. What remains is oxidation and a problem gasoline does not have: biology.
Chevron's diesel technical review notes that long-term storage stability "is of little concern to the average user, because most diesel fuel is consumed within a few weeks of manufacture," and that the chemistry of instability "often involves oxidation of the precursors," with "certain dissolved metals, especially copper" acting as catalysts (Chevron). Keep stored diesel out of contact with copper plumbing and fittings. Modern ultra-low-sulfur diesel is more stable against particulates but, because hydrotreating removes natural antioxidants, "may form peroxides during long-term storage" (Chevron).
The bigger issue for stored diesel is microbial growth. Refining sterilizes the fuel, but it "may quickly become contaminated if exposed to microorganisms present in air or water," and "because most microorganisms need free water to grow, biogrowth is usually concentrated at the fuel-water interface, when one exists." Static tanks "where fuel is being stored for an extended period of time, are a much better growth environment when water is present" (Chevron). The rule that follows is the same as for gasoline, only more so: keep water out. A sealed can, filled near full, stored cool, gives the organisms nothing to grow in. Biocides exist for tanks that already have a problem; a clean, dry can should never need one.
How to tell fuel has gone bad
Pour a little into a clear glass jar and look at it against the light. Fresh gasoline is pale and clear. Oxidized gasoline darkens toward amber and smells sour or like varnish rather than like gasoline. A cloudy haze means water in suspension; a distinct layer at the bottom means phase separation has already happened, and the EPA's description of what that layer does in an engine, running lean and hot in a four-stroke and starving a two-stroke of oil, is reason enough not to pour it in (EPA). Diesel that has grown something shows slime, dark sediment, or a rotten smell. Fuel in any of these states goes to a household hazardous waste facility, not a drain and not a fire pit.
Where the can fits in
Nothing above requires a particular brand of container. It requires a container that seals, holds pressure without distorting, and lets you keep headspace small. The Wavian 20L and 10L were designed around exactly those properties: 0.9 mm steel, a gasketed cam-lever cap with a locking pin, an internal breather pipe ending in a defined air pocket, and a fuel-resistant phenolic lining inside. Filled to the line, latched, pinned, and put on a shelf in a cool shed, it is the storage condition Chevron's one-year figure assumes. What size to store fuel in, and how much a full can weighs when you go to move it, is in Jerry Can Sizes Explained.
Frequently asked questions
How long does gasoline last in a jerry can?
In a can that seals, stored cool and out of the sun, Chevron's published answer is "at least one year." ExxonMobil's is six to twelve months. Both assume the container is closed, filled to about 95 percent, and kept at room temperature or below. Heat and a loose cap shorten that; a stabilizer added at fill time extends it.
Does gasoline go bad in a sealed container?
Slowly, yes. Even sealed, gasoline reacts with the oxygen in the headspace and forms peroxides and gums, which is why refiners blend in antioxidants. Sealing stops the faster losses: evaporation of the light ends that make the fuel easy to start, and moisture from the air. A sealed steel can with a gasket is about as good as a small container gets.
Can I use gasoline that is a year old?
If it was stored the way Chevron describes, closed and cool, they say it will retain its quality for at least a year. Use it in a vehicle rather than a small engine, which is less forgiving, and look at it first: darkened color, a varnish smell, or a separate layer at the bottom means it should go to household hazardous waste instead of an engine.
Do fuel stabilizers actually work?
Chevron's guidance is that if the container "will be in direct sun or will be heated above 30°C (80°F) much of the time, add an aftermarket fuel stabilizer when you fill it with gasoline." Stabilizers are antioxidants; they slow gum formation. They do nothing about a container that leaks vapor or lets water in. Follow the product's treat rate and add it to fresh fuel, not old fuel.
Is it safe to store gasoline in my garage?
The International Fire Code allows up to 10 gallons of flammable liquid in approved containers in a private garage without a storage cabinet, but cities adopt their own limits, and some are much lower. ExxonMobil's advice is a detached shed or garage, at least 50 feet from pilot lights and other ignition sources. Wherever it goes, keep it out of the sun, off the heat, and away from the water heater.
Does a steel can keep gasoline fresher than a plastic one?
What keeps fuel fresh is the seal and the temperature, not the material by itself. Where steel helps is that it holds a gasketed cam-lever seal for decades without the cap threads swelling or the body distorting in heat, and it does not let vapor migrate through the wall. The trade-offs in both directions are in Steel vs Plastic Gas Cans.
More storage, transport, and capacity questions are answered in the Jerry Can FAQ.
