How Long Does Gas Last in a Car?

Quick Answer

Gasoline sitting in a car's tank typically lasts 1 to 6 months before it starts to degrade. Standard gasoline stays fresh for about 3–6 months, ethanol-blended fuel (E10, the most common at U.S. pumps) for 1–3 months, and gas treated with a stabilizer can last 1–2 years. After that, fuel oxidizes, loses combustibility, and can gum up the engine.

Shelf Life by Fuel Type

Not all gasoline degrades at the same rate. Ethanol attracts moisture, which speeds up breakdown.

Fuel Type	Approximate Shelf Life
Regular gasoline (no ethanol)	3–6 months
E10 ethanol blend (typical pump gas)	1–3 months
E85 (high ethanol)	1–3 months
Gas with fuel stabilizer	1–2 years
Diesel	6–12 months

Factors That Affect How Long Gas Lasts

• Ethanol content: Ethanol absorbs water from the air (phase separation), which corrodes parts and shortens shelf life.
• Temperature and heat: Hot conditions accelerate evaporation of the volatile compounds that make gas ignite.
• Air exposure: A partially full tank has more air, promoting oxidation. A full, sealed tank lasts longer.
• Container seal: In portable cans, a tight seal dramatically slows degradation.
• Fuel quality: Higher-octane and "top-tier" fuels sometimes contain additives that resist breakdown slightly better.

Signs Gas Has Gone Bad

• A sour, varnish-like, or unusually strong smell
• Darker color than fresh gasoline
• Engine that's hard to start, runs rough, sputters, or stalls
• Check-engine light after sitting for months

How to Keep Gas Fresh Longer

1. Fill the tank before long storage to minimize air and condensation.
2. Add a fuel stabilizer (like Sta-Bil) for anything stored more than 30 days; it can extend life to a year or more.
3. Store in a cool, shaded place away from temperature swings.
4. Run the engine briefly every few weeks so fresh fuel circulates through the system.
5. For seasonal vehicles, either fill and stabilize the tank or run it nearly dry before storage.

If Your Gas Is Old

If fuel has sat for many months, don't just start the car and hope. For mildly old gas, topping off with fresh fuel dilutes it enough to burn safely. For clearly degraded gas, the tank should be drained and the fuel disposed of at a hazardous-waste facility — never poured down a drain or onto the ground. Running badly degraded fuel risks clogging injectors and damaging the fuel system.