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A dual fuel generator lets you run on gasoline or liquid propane (LP), and each has a clear job. Gasoline gives you a little more peak power; propane runs cleaner, stores for years, and is easy to keep on hand for emergencies. Here's how they compare on power, cost, and runtime — with simple rules of thumb.
Because gasoline is more energy-dense than propane, a dual fuel generator produces a bit more peak wattage on gas than on propane — the manufacturer lists both numbers on the spec sheet. If you're right at the edge of your surge needs (starting a well pump or AC), gasoline gives you a small margin. For most loads the difference is minor.
Which is "cheaper" per hour swings with local fuel prices, so compare cost per usable energy, not per gallon. Propane is priced per gallon but carries less energy per gallon than gasoline, so a gallon of propane usually runs the generator a shorter time than a gallon of gas. When gasoline prices spike, propane can win; when propane is expensive, gas wins. The bigger cost advantage of propane is that it doesn't degrade in storage.
Runtime depends on load and tank size. A useful rule of thumb: a standard 20 lb (5-gallon) propane tank holds roughly 430,000–460,000 BTU, and a mid-size generator at half load often draws it down in about 5–10 hours. Scale up for bigger tanks:
The honest answer for any specific unit is on its data sheet (it lists run time at 25%/50% load for each fuel). To go longer, use a larger propane tank or switch to a tri fuel model on natural gas — see our dual fuel vs tri fuel guide.
Propane burns cleaner, which means fewer carbon deposits and no stale-fuel problems — a real plus for a unit that mostly sits waiting for an outage. Gasoline needs stabilizer and ideally should be run down or rotated. Many owners store the generator ready on propane and keep gasoline as the on-the-go option.
Shop units that give you both options in our dual fuel generators collection, or see the full generators range. For silent, fuel-free backup that complements a generator, browse portable power stations.
Is it better to run a dual fuel generator on gas or propane?
Gas for a bit more peak power and on-the-go use; propane for clean, long-storage emergency backup. Many owners keep it on propane for standby.
Is it cheaper to run a generator on propane or gas?
It depends on local prices. Propane has less energy per gallon, so compare cost per hour, not per gallon. Propane's edge is that it doesn't go stale in storage.
How long will a 20 lb propane tank run a generator?
Roughly 5–10 hours at moderate load on a mid-size unit; check the model's data sheet for exact figures.
What are the downsides of a propane generator?
Slightly lower peak power than gasoline, dependence on tank supply, and reduced output in very cold weather (propane vaporizes less readily when it's freezing).
Can a dual fuel generator run 24 hours a day?
It can run for extended periods with adequate fuel and oil, but follow the manufacturer's guidance on cool-down and maintenance intervals, and never run it indoors.
This article is general information and uses rounded rules-of-thumb; actual power, cost, and runtime depend on your specific generator, load, fuel prices, and conditions. It is not professional advice. Always follow the manufacturer's manual and local codes, and never operate a generator indoors or in an enclosed space.