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Gas Myth: Does Gas Expire?

Has it been a while since you’ve hopped in the car and gone for a drive? Are you ready to retire your lawnmower as winter creeps closer? If so, you might be thinking about your gas and wondering if it has a shelf life. Let’s take a closer look at gasoline, what it’s made up of, and what you can do to make it last:

Does Gasoline Actually Expire?

Long story short: yes, gasoline really can go bad. However, there is no hard and fast rule as to when it will expire. Many factors play into how long gasoline is “good” for, including how it’s stored, ethanol levels, the time of year, and more. Generally, properly stored gas can last between 3 to 6 months; if you add fuel stabilizers, you can extend its shelf life by a year or so (under optimal conditions, of course). That gas in your car’s tank, however, will more than likely start degrading in about a month.

The Unique Makeup of Gasoline

We know what you might be thinking – if crude oil can last for millennia, why does gasoline have such a short shelf life? That’s because gasoline is a much different substance than crude oil by the time you purchase it.

Gasoline is made up of a complex cocktail of carbon and hydrogen atoms, which bond together to create combustive hydrocarbons that make engines run. As petroleum is refined, impurities like sulfur are removed and additives like ethanol are added to improve the substance’s performance. The end product is an amalgamation of various compounds that work together to help power your vehicle of choice.

The 3 Big Gas Degradation Factors

In time, gasoline will begin to change and won’t perform as well as you hope. This is thanks mostly to three big environmental factors: oxidation, water, and evaporation.


You might recall that we mentioned oxygen as one of the main ingredients in combustion – but it also causes oxidation. As the weeks and months go by, oxygen molecules in your gasoline will begin tapping healthy hydrocarbons and changing their structure, leading to increased oxidation. You know what that means – combustion isn’t nearly as impressive (or efficient).


What happens when you put ice cubes in a glass of soda and you don’t even drink it? Your beverage becomes diluted (and way less tasty, in our opinion). In the same vein, you never want to have additional water in your gasoline, but there’s one compound that doesn’t like to play by the rules: ethanol.

Most gasoline in the United States has a certain level of ethanol – usually 10% (E10 for short). Unfortunately, ethanol is quite charming and attracts water molecules in the air around it, which in turn shortens gasoline’s shelf life. The higher the ethanol level, the faster your gas will expire.


Guess what? Some hydrocarbons are heavier than others – and the lighter ones evaporate more quickly. Remember when we talked about summer and winter fuel blends? In a nutshell, summertime gasoline has heavier hydrocarbons since the hot temperatures evaporate lighter molecules, and winter gasoline has lighter hydrocarbons to make your engine run more smoothly in the cold. More evaporation means more oxidation!

Why You Shouldn’t Use Old Gas

Maybe you’re reading this blog and thinking, “Okay, so what’s the big deal if I use old gas?” If you treasure your vehicle and its hard-working engine, you’ll want to think twice before using old gasoline. As gasoline begins to deteriorate, it becomes more solid and forms a gummy substance. If the gum enters your engine, it can easily clog the lines and wreak some havoc on the internal components.

In short, if you want to keep your vehicle in good shape and save money in the long run, don’t use old gasoline!

How to Identify Expired Gas

Looking for a quick way to determine if your gas has gone bad? Expired gas tends to be darker in color and gives off a sour smell. A quick sniff test should help you figure out if your gas is past its prime. Of course, you can make your life easier by properly storing and labeling your gas!

How to Make Gasoline Last

We all want to do what we can to make our fuel last as long as possible. Here are a few pro-tips to help you make it last:

  • Store gasoline in a clean, airtight, gasoline-approved storage container in a cool or room temperature environment.
  • Avoid high ethanol blends, especially if you don’t plan on using the motor frequently.
  • Consider using a fuel stabilizer additive to keep gas potent and fresh in an idle vehicle or piece of machinery.


You can always count on HSO to deliver fresh, high-quality fuel quickly and efficiently to your business, farm, or construction site whenever you need it. Running low on gas? Visit your local Express Mart, a proud division of HSO. Call us today at 1-800-467-5044 to learn more or request our services!




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