Gasoline vs. Propane vs. Dual Fuel: What to Actually Run
Gasoline is everywhere but goes stale in months. Propane keeps for decades but costs you ~10% of output. Why dual fuel wins for outage kits.
Updated July 15, 2026
Fuel choice sounds like a spec-sheet detail until the first multi-day outage, when it becomes the whole problem. The generator that runs is the one with fuel you can actually get — or better, fuel you stored two years ago that's still good. Here's how the three options behave in the real world.
Gasoline: maximum power, minimum shelf life
Every generator makes its full rated output on gasoline, and every gas station sells it — until the power's out regionally, at which point stations without backup power can't pump, and the ones that can grow hour-long lines. The bigger everyday problem is storage: pump gas with ethanol starts degrading in about a month and is genuinely stale by three to six, and stale gas varnishing the carburetor is the number-one reason generators fail to start. If you store gasoline, add fuel stabilizer the day you buy it, rotate cans into your car every few months, and run the carb dry before the machine goes back on the shelf.
Propane: the fuel that waits for you
Propane in a sealed cylinder is still perfect fuel twenty years from now. It burns clean (no carb gumming, longer oil life), it's exchangeable at every hardware store, and cylinders stack quietly in the garage — that's why it's the outage-prep fuel. The costs: expect roughly 10% less output than the same unit on gasoline (check the published propane rating, not the headline number), somewhat fewer watt-hours per dollar, and regulators that get sluggish in deep cold. A 20 lb cylinder runs a mid-size unit roughly 5–8 hours at half load; serious storm coverage means several cylinders or a 100 lb bottle.
Dual fuel: the pragmatic answer
Dual-fuel units run either, switchable in seconds. The strategy that makes them the default recommendation for outage kits: store propane (it keeps forever), and treat gasoline as the surge fuel you grab when you need full output or the cylinders run out. You pay a modest price premium and carry a slightly more complex fuel system, and in exchange your stored fuel can't go bad and your supply chain has two paths instead of one.
| Gasoline | Propane | Dual fuel | |
|---|---|---|---|
| Output | 100% of rating | ~90% of gas rating | Both, switchable |
| Shelf life | 1–6 months (stabilized: ~1 yr) | Decades | Store propane, buy gas fresh |
| Availability in a regional outage | Poor — pumps need power | Good — sealed cylinders in stock | Best of both |
| Engine cleanliness | Carb varnish risk | Very clean | Clean on LP |
| Cold weather | Fine | Regulator sluggish below ~0°F | Use gas when frigid |
Natural gas deserves a mention: some large portables and nearly all standby units can run on it, which means never refueling at all. The trade is another ~10% output derate versus propane and a plumber on the install bill — the right call when the machine lives permanently beside the house.
Frequently asked questions
How long can I store gasoline for my generator?
Untreated ethanol pump gas is reliable for one to three months. With stabilizer added the day you buy it, plan on six months to a year. The practical system: keep two cans, stabilized and dated, and pour them into your car every few months, refilling fresh — your stored fuel is always young.
How much propane does a generator use?
Rule of thumb: a mid-size (3,000–5,000W) unit at half load burns roughly 0.5–0.9 gallons of propane an hour, so a standard 20 lb cylinder (about 4.6 gallons) is good for 5–8 hours. The big 7,500W-class machines at half load drain a 20 lb bottle in about 4–5 hours — storm prep means multiple cylinders.
Why does my generator make less power on propane?
Propane carries less energy per unit of intake air than gasoline vapor, so the same engine develops roughly 10% less power on LP. Manufacturers publish separate propane ratings for exactly this reason — size your load against the propane figure if propane is your primary fuel.
Is dual fuel worth the extra cost?
For outage preparedness, almost always. The premium is typically $100–$250, and it buys you a stored fuel that can't go stale plus a second supply chain when gasoline is scarce. For a generator used mainly for camping or job sites with fresh gas, single-fuel is fine and slightly simpler.