Dual-Fuel vs Gasoline vs Propane Generators: Running Costs Compared

Picking the generator type gets all the attention. Picking the fuel gets almost none — and it’s the choice that determines what your backup power actually costs to run, whether it starts after sitting for a year, and whether you can even get fuel during the outage you’re preparing for.

Three fuels, three different tradeoffs. Here’s each one straight.

Gasoline: The Default (With Strings Attached)

Most portable generators run on gasoline. The units are the cheapest to buy, and gas is everywhere — until it isn’t.

The real problems with gasoline:

• It goes stale. Untreated gasoline starts degrading in 30 days and is unreliable by 3–6 months. The varnish it leaves behind gums up carburetors — the single most common reason a generator won’t start when needed. Fuel stabilizer (Sta-Bil or equivalent) extends storage to 12–24 months, but “add stabilizer and forget it” still fails if you never rotate the stock.
• Running cost is the highest. Gasoline is the most expensive fuel per unit of energy of the three, and portable generators burn through it: a 7,500W unit at half load drinks roughly 0.8–1.0 gallons per hour.
• Availability collapses in real outages. Gas stations need electricity to pump. After a hurricane or ice storm, stations without power can’t sell you fuel no matter how much is in their tanks. The lines at the stations that do have power are the stuff of local legend.

Where gasoline still wins: it’s the highest-energy option of the portable fuels, so you get the generator’s full rated wattage. If you already keep fresh gas on hand for lawn equipment and you’re disciplined about rotation, it’s the simplest fuel to live with.

Propane: The Storage King

Propane (LPG) is the same fuel as your grill tank. For generators, it’s usually supplied from 20-lb grill cylinders or larger 100-lb/100-gallon tanks.

Why people switch to propane:

• It never goes stale. Propane doesn’t degrade, gum up, or varnish. A tank can sit for ten years and the fuel is exactly as good as day one. For the “might need it once a year” generator owner, this is the killer feature.
• Cleaner burning. Less carbon buildup, longer oil life, easier on the engine. Propane generators typically go longer between oil changes than gasoline equivalents.
• Safer storage profile. Propane tanks are sealed and pressurized — no fumes, no spills, no vapor creeping along the floor toward a pilot light.

The tradeoffs:

• About 10% less power. A generator rated 9,500W on gasoline typically delivers around 8,500–8,600W on propane. Propane has less energy per unit volume. Size accordingly — if you need the full rating, buy a bigger unit or stick with gas.
• Tank logistics. A 20-lb grill tank holds about 4.6 gallons of propane. At typical consumption, that’s 4–6 hours of runtime on a mid-size generator. For a multi-day outage you need multiple tanks or a large stationary tank — and refilling requires a propane dealer, not a gas station.
• Cold weather. Propane vaporization slows in extreme cold. Below about -20°F/-29°C, a 20-lb tank struggles to feed a big generator. Larger tanks or tank warmers solve it, but it’s a real consideration in northern winters.

Natural Gas: Unlimited Runtime (If You Have the Pipe)

Natural gas is almost exclusively a standby-generator fuel — portables don’t connect to it. If your house has a gas line, a standby unit taps in and runs as long as the utility flows.

The case for it: unlimited runtime without refueling, no tanks to monitor, no trips to buy fuel in a storm, and the lowest fuel cost per hour of the three. A 22 kW standby on natural gas costs roughly $2–$4/hour to run at typical loads.

The honest risks:

• Lowest power output. Generators derate most on natural gas — typically 10–15% below the gasoline rating. Manufacturers publish separate NG ratings; use those, not the headline number.
• The utility can shut it off. In earthquakes, major infrastructure damage, or utility-declared emergencies, gas service can be interrupted. It’s rare, but it’s the one scenario where your “unlimited” fuel isn’t.
• You’re locked in. No gas line to your house? Running one just for a generator is usually not worth the cost. And you can’t take the fuel with you — it’s a permanent installation decision.

Dual-Fuel: The Hedge

Dual-fuel generators (Champion pioneered the affordable ones; Westinghouse, DuroMax, and Predator now all offer them) run on gasoline or propane with a selector switch. The premium over gasoline-only is typically $50–$150 on a mid-size portable.

This is the option I recommend most for portable buyers, and here’s why: fuel flexibility is outage insurance. Run gasoline when it’s fresh and available; switch to propane when the gas is stale, the stations are dark, or you just want the cleaner-burning option. You get propane’s infinite storage life as your backup plan and gasoline’s full power rating when you need every watt.

The only real downside is the same propane derating — you lose ~10% output on propane. But having the choice beats having the perfect fuel you can’t get.

What about tri-fuel?

A few manufacturers (DuroMax’s XP13000HXT and similar) now sell tri-fuel units that add natural gas to the gasoline/propane mix, usually via a quick-connect hose to your home’s gas line. The concept is appealing — three options instead of two — but be honest about what you’re buying: a portable that can sip from the house gas line still needs you home to start it, still needs extension cords or a transfer switch, and natural gas derates output the most of the three fuels (~15%). Tri-fuel makes sense in exactly one scenario: you have a gas line with an accessible outdoor connection and you want portable flexibility with unlimited-runtime potential. For most buyers, dual-fuel plus a propane stockpile is the simpler, cheaper answer.

Running-Cost Math: 7,500W Generator at Half Load

Numbers for a typical 7,500W portable running ~3,750W (half load), using approximate 2026 US fuel prices:

A few things these numbers tell you:

• Gasoline is the most expensive portable fuel to run, even though the generator was cheapest to buy. The cheap unit is a trap if you run it a lot.
• Natural gas is the cheapest per hour — one of the quiet economic arguments for standby units in areas with frequent outages.
• A three-day outage on a portable costs $200–$275 in fuel alone. Budget for it. People buy the $900 generator and forget the $250 fuel bill and the five gas cans.

(These are approximations — your local fuel prices and your generator’s actual consumption curve will move the numbers. Check your unit’s spec sheet for its rated consumption at 50% load.)

Storage and Safety

Practical storage rules:

• Gasoline: stabilizer at purchase, rotate every 6–12 months, keep 10–25 gallons on hand depending on your outage risk. Metal safety cans beat plastic for long storage.
• Propane: 20-lb tanks are fine for short outages; for multi-day coverage, a 100-lb cylinder (~23 gallons) or a leased 100–250 gallon stationary tank from a propane dealer. Check tank certification dates — tanks need recertification every 10–12 years.
• Natural gas: nothing to store. But know where your gas shutoff valve is, and keep the utility’s emergency number accessible.

Planning Your Fuel Stockpile

Don’t buy the generator and figure out fuel later. Size the stockpile to your outage risk:

• Low risk (a few short outages a year): 10–15 gallons of stabilized gasoline or two 20-lb propane tanks. Either covers a day of essentials.
• Medium risk (annual storm season, 1–3 day outages): 25–40 gallons of gasoline with a rotation plan, or four 20-lb propane tanks / one 100-lb cylinder. This is the dual-fuel sweet spot — split between both fuels so a shortage of one doesn’t strand you.
• High risk (hurricane/ice-storm country, week-long outages): standby on natural gas if available. If not, a 100+ gallon propane tank (leased from a dealer, auto-refill contract) feeding a dual-fuel portable or a propane standby.

One more practical note: buy fuel containers before the storm, not during. Gas cans sell out alongside the generators. And fill your car’s tank when a storm is forecast — in a pinch, 15 gallons in the car is a reserve you already own.

Which Fuel for Which Outage Pattern

• Occasional short outages (a few hours, few times a year): dual-fuel portable, kept on propane. Zero fuel-maintenance headaches, gasoline available as the backup option.
• Frequent or seasonal outages (storm country, hurricane/ice season): dual-fuel portable with a real propane stockpile (multiple 20-lb tanks or a 100-lb cylinder) plus stabilized gasoline. Or a standby on natural gas if the budget allows.
• Multi-day outage risk: standby on natural gas is the gold standard for runtime. If that’s out of budget, a large dual-fuel portable with 40+ gallons of propane equivalent is the practical answer.
• Whole-home, set-and-forget: standby on natural gas (or propane with a large tank if no gas line). This is the standby generator use case.

The Bottom Line

For most portable-generator buyers, dual-fuel is the right call — the small upfront premium buys you out of gasoline’s two worst problems (stale fuel and outage availability). For standby buyers with a gas line, natural gas wins on running cost and convenience. Propane-only makes sense when you have no gas line but want a standby’s permanence with a fuel that stores forever.

Whichever fuel you choose, the generator still needs maintenance — fuel system care is half the battle. See the generator maintenance checklist for the schedule, and if you’re still deciding on the machine itself, start with the pillar guide: home backup power explained.