Does Gasoline Go Bad?

The chemicals that give gasoline its combustibility also limit its shelf life.

Ronan Glon | 

Jun 14, 2024 | 3 min read

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Movies depicting postapocalyptic societies sometimes show a car roaring to life years after the collapse of civilization — but that particular scenario, at least, is one that is unlikely to ever happen. Even if we assume the engine is in running condition, the gasoline in the tank would probably have gone bad and be far too old to burn. Here's why gasoline goes bad and how long you typically can store it.

The Ingredients of Gasoline

Gasoline is a blend of processed crude oil that includes more than 100 hydrocarbons as well as chemicals that prevent rust. Ethanol-blended gasoline, such as E10 or E85 (which contain 10 and 85 percent ethanol, respectively), has become increasingly common across the U.S. The term unleaded is obsolete because all gasoline is unleaded today; leaded gasoline was phased out entirely in 1996.

Why Gasoline Goes Bad

Whether your car requires E85 or premium 91-octane gasoline, the chemicals that make up the fuel break down over time and lose their properties. This is the natural result of many chemical reactions.

Gasoline begins to evaporate when it's stored for a prolonged period, and the more volatile hydrocarbons evaporate first so the fuel becomes more difficult — and less efficient — to burn. The hydrocarbons that are left degrade over time as well. It's this process that causes gasoline to "go bad."

Oxidation happens when oxygen comes in contact with gasoline. It breaks down the hydrocarbons and forms deposits that clog parts of the fuel system, such as the filter and the injectors, and cause your car to run poorly. Hydrolysis is a separate process that occurs when moisture, like humidity, mixes with fuel. The fuel then becomes corrosive and allows rust to form. In turn, rust can damage parts of your car's fuel system, and its particles can have a similar effect to oxidation's deposits.

While diesel normally lasts longer than gasoline, its shelf life isn't eternal. As diesel ages, it can develop a sludge-like substance made up of mold, bacteria, and fungus that wreaks havoc on the fuel system.

How Long Can You Store Gasoline?

The shelf life of gasoline depends on the type of fuel you're storing and how it's stored. Ethanol-blended gasoline ages faster than regular unblended gasoline because ethanol absorbs water. That water contaminates the fuel, makes it more difficult to burn, and further increases the likelihood of damaging the fuel system. In a car's fuel tank, gasoline that contains ethanol can go bad anywhere between a month and a few months.

You can store regular gasoline for up to about six months in airtight containers. Diesel can be stored for more than a year in the right conditions.

Fuel stabilizer extends the shelf life of gasoline by slowing down the chemical reactions that cause it to go bad. It's sold in many hardware stores and auto-parts stores, and it can cost less than $20 for enough to treat your vehicle's gas tank if you plan to store it for a while. But it probably won't outlast the apocalypse.

Ronan Glon

Ronan Glon is an American journalist and automotive historian based in France. He enjoys working on old cars and spending time outdoors seeking out his next project car.