How to Store Gasoline for a Generator Long-Term
Quick answer
Regular gas goes bad in 30 days. Add a fuel stabilizer (STA-BIL) to fresh gas and you get 12–24 months of safe storage. Use an approved red gas can or metal jerry can, store it in a detached garage or shed — not your house — and rotate your supply every 6–12 months. That's the whole system.
Why Generator Gas Goes Bad (And Why It Matters)
Most portable generator problems — hard starting, backfiring, rough running — trace back to one root cause: stale gasoline. Here's what actually happens inside your fuel system when gas degrades:
- 1
Ethanol absorbs moisture from the air
Standard E10 gas (10% ethanol) is hygroscopic — it pulls water out of the air and into your fuel. Water doesn't burn. It causes misfires, corrosion, and phase separation where water sinks to the bottom of the tank.
- 2
Oxidation leaves varnish deposits
As gas oxidizes, it thickens and leaves a sticky brown varnish on carburetor jets, needle valves, and float bowls. This restricts fuel flow, causing lean-run conditions, hard starting, and backfires.
- 3
The engine may not start at all
After 60–90 days of untreated storage, varnish deposits can block fuel flow completely. The generator cranks but won't fire — a carburetor cleaning or replacement is the only fix at that point.
90% of generator shop repairs are caused by stale fuel. Proper storage costs under $15 in supplies. A carburetor replacement costs $80–$250 plus labor. The math is simple.
Gas Shelf Life: How Long Does Each Type Last?
| Fuel Type | Without Stabilizer | With STA-BIL | Notes |
|---|---|---|---|
| Regular 87-octane (E10) | 30 days | 12–24 months | Most common — use with stabilizer |
| Premium 91–93 octane (E10) | 30 days | 12–24 months | No benefit over 87-octane for generators |
| Ethanol-free (E0 / pure gas) | 3–6 months | 24+ months | Best choice — no moisture absorption |
| TruFuel pre-mixed | 2+ years (sealed) | N/A | Expensive but truly shelf-stable |
| Propane (LP) | Indefinite | N/A | No degradation — for dual-fuel generators |
* Shelf life depends on storage temperature and seal quality. Cool, dark storage extends life; hot direct-sun storage shortens it.
The 5-Step Generator Fuel Storage Protocol
Follow this once per season and you will never have a stale-fuel problem.
- 1
Buy fresh fuel — and note the date
Purchase 87-octane non-ethanol (preferred) or regular E10 from a high-volume station with fast turnover. Write the purchase date on the container with a permanent marker. Gas sitting in station tanks for weeks is already partly degraded.
- 2
Add stabilizer immediately
Add STA-BIL 360 at the ratio on the label (1 oz per 2.5 gallons) before the gas goes into your storage containers or generator tank. Shake gently to mix. Adding stabilizer to already-old gas does not reverse degradation — it must go into fresh fuel.
- 3
Fill approved containers, leave 5% headspace
Use only UL-listed or FM-approved red plastic cans or metal NATO jerry cans. Fill to 95% capacity — not all the way to the brim. Gasoline expands with heat; no headspace means spills and pressure buildup.
- 4
Store in a detached garage or outdoor shed
Never store inside the house, near water heaters, furnaces, electrical panels, or dryers. Gasoline vapors are heavier than air and settle near the floor — any ignition source within 50 feet is a risk. Check your local fire code for maximum quantities (typically 25 gallons residential).
- 5
Rotate every 6–12 months
Even with stabilizer, rotation is best practice. Dump your stored fuel into your car's gas tank (it blends fine with fresh pump gas), then refill your storage containers with fresh stabilized fuel. Label the date each time. This keeps your emergency supply always within its prime window.
Container and Location Rules at a Glance
Do This
- Use UL-listed red plastic or metal jerry cans
- Store in detached garage or outdoor shed
- Keep in cool, dark, well-ventilated area
- Add stabilizer to every new batch
- Label containers with the purchase date
- Leave 5% headspace for expansion
- Rotate supply every 6–12 months
Never Do This
- Store gas inside your home or apartment
- Use milk jugs, water bottles, or unapproved containers
- Store near pilot lights, furnaces, or dryers
- Fill containers all the way to the brim
- Add stabilizer to fuel older than 30 days
- Store more than your fire code allows
- Keep gas directly in sunlight or heat
What You Actually Need
Three items cover everything — stabilizer, a proper container, and an optional premium-grade alternative.
STA-BIL 360 Protection
8 oz treats 40 gallons · up to 24 months storage
~$12
- Prevents ethanol damage and moisture
- Works in all gas-powered small engines
- Add to every batch — not just winter storage
- Also protects fuel lines and carb diaphragms
No-Spill 5-Gallon Can
UL-listed · pressure-equalized spout · CARB compliant
~$25
- No dripping or spilling — child-proof spout
- Passes CARB vapor emissions standards
- Vented design prevents over-pressurization
- Stores flat without leaking
Wavian 20L NATO Jerry Can
Steel · UN-approved · 5.3 gallons · vented cap
~$75
- Military-grade steel — no plastic degradation
- Designed specifically for long-term fuel storage
- UN/DOT approved for transport and storage
- Nested handle for easy pouring
Already have old gas in your generator? Here's what to do.
If your generator has been sitting with untreated fuel for more than 30–60 days, the damage has already started. Draining and refueling is step one — but if the carb is already gummed up, you'll need to clean or replace it. The symptoms are hard starting, rough running, or backfiring.
Frequently Asked Questions
How long can you store gasoline for a generator?
Regular 87-octane gasoline (E10, with 10% ethanol) degrades in as little as 30 days without a fuel stabilizer. The ethanol in blended gas absorbs moisture from the air, which accelerates breakdown and leaves a varnish residue that clogs carburetor jets. With a quality fuel stabilizer like STA-BIL 360, properly sealed gasoline can last 12–24 months. Ethanol-free gasoline (E0, available at some marinas and small-engine dealers) lasts 3–6 months without stabilizer and 2+ years with it.
Does fuel stabilizer actually work for generator storage?
Yes — fuel stabilizer genuinely extends gasoline shelf life by preventing oxidation and neutralizing the corrosive effects of ethanol. STA-BIL 360 Protection is the most widely tested formula; it treats up to 40 gallons with a single 8-oz bottle and is safe for all carbureted and fuel-injected small engines. The key is to add the stabilizer to fresh fuel, not to already-degraded gas. If your fuel is more than 30 days old without stabilizer, it is too late — drain and replace it.
Where is it safe to store gasoline at home?
The safest location is a detached garage or outdoor shed, away from any ignition sources (water heater pilot lights, furnaces, electrical panels, dryers). Never store gasoline inside your living space — vapors accumulate even through sealed containers. Keep containers in a cool, shaded area; heat above 80°F accelerates degradation and increases vapor pressure. Most local fire codes allow up to 25 gallons of gasoline in an approved container at a residential property — check your municipality's specific limit.
What is the best gas can for storing generator fuel?
For gasoline storage, use only UL-listed or FM-approved containers. The No-Spill 5-gallon can is the best consumer option — its pressure-equalized spout eliminates spillage and dripping. For larger quantities, a steel NATO-style jerry can (10–20 liters) is the most durable option, designed for long-term military fuel storage. Avoid generic red plastic cans with flip-up spouts — they commonly drip, don't seal well, and some are not ANSI-compliant. Never store fuel in old milk jugs, water bottles, or non-approved containers.
Should I store my generator with gas in the tank or empty?
For storage longer than 30 days: add fresh fuel + stabilizer, run the generator for 5 minutes to circulate the treated fuel through the carburetor, then store it full. Do NOT store with untreated old fuel — it gums up the carburetor. Alternatively, drain the tank and carburetor completely (run the engine until it dies from fuel starvation) and store it bone dry. Both methods work; treated-full is more common and the engine starts more easily in an emergency. Empty-dry is preferred for multi-year storage.
Is ethanol-free gas better for generator storage?
Yes, significantly. Ethanol-free gasoline (E0 or 'pure gas') does not absorb moisture, resists degradation far longer, and leaves no corrosive residue in the fuel system. It costs 20–50 cents more per gallon and is available at marinas, small-engine shops, and select gas stations (findable via pure-gas.org). For generator storage, ethanol-free gas is the best choice. If you can't source it, regular E10 with a fuel stabilizer is the next best option — just rotate your supply every 6–12 months.
Picking the right generator size in the first place?
Add your appliances and get an instant wattage recommendation — so you buy the right size generator before you need it.
Open Wattage CalculatorNeed a quick reference? Download our free Wattage Cheat Sheet — 50+ appliances with starting & running watts