Generators run on four fuels: gasoline, propane (LPG), natural gas (NG), and diesel. The differences between them aren't just about what you happen to have on hand — they ripple through nearly every aspect of generator ownership, from runtime and storage to cold-weather behavior, fuel cost per kilowatt-hour, noise, and maintenance schedules.
This is the comparison most buyers wish they'd seen before choosing a generator, because the right answer depends entirely on use case. Here it is.
The headline trade-offs
| Fuel | Best for | Weakness |
|---|---|---|
| Gasoline | Maximum portability, lowest sticker price | Fuel degrades; pumps fail during outages |
| Propane | Long-term storage, cleaner burn, quiet | 10–15% less power; cold-weather starting |
| Natural gas | Standby units; unlimited supply | Not portable; less common in portable units |
| Diesel | Heavy-duty continuous duty, fuel efficient | Expensive units; cold-weather gelling |
Gasoline
The default fuel for portable generators. Almost every consumer-grade portable generator comes in a gasoline-only or dual-fuel (gas + propane) configuration.
Strengths. Gasoline engines start easily across a wide temperature range. Refueling at gas stations is convenient under normal conditions. Wattage per dollar of generator is highest with gasoline-only units — adding propane capability typically increases generator cost by $150–300. Power output on gasoline is the rated number; on propane, the same generator delivers 10–15% less.
Weaknesses. Gasoline degrades quickly. Untreated pump gas (E10) starts to deteriorate in 30 days and reliably gums up carburetors by 60–90 days. With stabilizer, you can stretch storage to 12–24 months. The bigger problem during emergencies: gas pumps need electricity, and during widespread outages they're down. Hurricane Sandy, the 2021 Texas freeze, and most regional disasters produce 24–72 hours of empty gas stations precisely when you need fuel.
Storage: 5-gallon NATO-style metal cans or HDPE plastic cans rated for gasoline. Store away from the house in a shed or detached garage. Annual fuel rotation is the minimum even with stabilizer — burn off old stored fuel in the lawn mower or car before topping off with fresh gas. Most homeowners store 10–25 gallons of gasoline for a generator with the math working out to about 24–72 hours of runtime at typical loads.
Runtime example: A 7,500W generator at 50% load (3,750W) burns about 0.6–0.8 gallons per hour. A 6-gallon tank runs 8–10 hours; 25 gallons of stored fuel runs 30–40 hours total.
Propane (LPG)
Propane has emerged as the preferred fuel for home backup generators not because it's better at producing electricity (it's slightly worse, per pound), but because of storage.
Strengths. Propane stores indefinitely. A 20-pound BBQ tank you bought five years ago is still ready to run. There's no fuel degradation, no carburetor gumming, no need for stabilizer. Propane burns cleaner than gasoline, leaves less carbon deposit on the spark plug and exhaust valve, and engines that run primarily on propane often go longer between major service.
Propane is quieter — both because the combustion is smoother and because dual-fuel generators sometimes have slightly less aggressive throttle response on propane. Propane is also non-spillable, which makes it safer to handle and store in attached garages where gasoline can't go.
Weaknesses. Wattage drops 10–15% on propane vs the same generator on gasoline. So a "7,500W dual fuel" delivers roughly 7,500W on gas and 6,375–6,750W on propane. This matters when sizing: spec the generator for propane wattage if propane will be your primary fuel.
Cold-weather starting can be harder below 32°F. Propane regulators can freeze in extreme cold, and the BTU output per pound of liquid propane drops as ambient temperature falls. Below -10°F, propane operation becomes unreliable without a regulator heater.
Refilling is less convenient than pumping gas — you exchange or refill tanks at specific propane stations or hardware stores. Smaller, more rural areas may have limited refill capacity. Larger 100-gallon ASME tanks installed at the house ($800–1,500 installed) solve this for serious users.
Runtime example: A 7,500W dual-fuel generator at 50% load burns about 1 gallon of propane per hour (propane is less energy-dense per gallon than gasoline). A 20-pound BBQ tank holds about 4.7 gallons, so it runs roughly 4–5 hours at moderate load. A 100-gallon ASME tank runs 100+ hours at the same load — multi-day backup without refueling.
Natural gas (NG)
Natural gas is the standard fuel for standby/whole-house generators, but it's also available in some tri-fuel and dual-fuel portable generators (typically requiring a separate adapter and a low-pressure regulator from the house gas line).
Strengths. Unlimited supply — as long as your natural gas service stays up, the generator runs indefinitely. No refueling, no storage, no fuel rotation. Cleanest-burning of the four fuels. Used appropriately, a natural-gas standby unit can run for weeks without intervention.
Weaknesses. Natural gas service can fail during the same disasters that cause power outages — pipeline damage from earthquakes, freezing during severe cold (Texas, 2021), service shutoffs during fires. A natural-gas-only generator is at the mercy of utility infrastructure. Tri-fuel units that can switch to propane or gasoline solve this.
Wattage drops further on NG than on propane — typically 20–25% below the gasoline rating, because natural gas is less energy-dense. Spec accordingly. Portable generators marketed as "natural gas compatible" generally require a conversion kit and connection to a fixed gas line — you can't really carry one and tap into NG service wherever you go.
Diesel
Diesel generators are rare in the portable/consumer market and dominant in commercial, marine, and large standby applications. Some 6,000W+ portable diesels exist (Generac XD5000E, several Kubota- and Yanmar-powered units in the contractor segment), but they're a small slice of the market.
Strengths. Diesel engines are mechanically simpler and more durable than gasoline equivalents — they don't have spark plugs, ignition coils, or carburetors to fail. Diesel has higher energy density than gasoline (a gallon of diesel produces about 10% more kWh than a gallon of gasoline). Diesel engines also achieve much longer service intervals — 1,000+ hours between major maintenance is normal.
Diesel fuel stores better than gasoline — 6–12 months with stabilizer (longer with biocide additives), compared to gasoline's 30–60 day untreated shelf life. Commercial diesel standby units are routinely sized for weeks of operation per tank.
Weaknesses. Sticker price. A 6,000W diesel portable runs $2,500–5,000 vs $700–1,200 for an equivalent gasoline unit. The economic justification only works for users who run the generator hundreds of hours per year — contractors, off-grid homesteaders, mobile food operations.
Cold-weather operation requires consideration: diesel gels below 0°F to -15°F depending on the fuel, requiring winter-blend diesel or a fuel-line heater. Diesels are loud — comparable to or louder than conventional gasoline generators of the same size, with a distinctive lower-frequency rumble.
Cost per kWh produced
At typical mid-2026 fuel prices, the rough cost-per-kWh ranking is:
| Fuel | Approximate cost per kWh produced | Notes |
|---|---|---|
| Natural gas | $0.08–0.15 | Lowest, where service is available |
| Gasoline | $0.30–0.45 | Varies with pump prices |
| Propane | $0.35–0.55 | Refill price varies; bulk delivery cheaper |
| Diesel | $0.30–0.40 | Higher fuel cost offset by efficiency |
| Solar (no fuel) | $0.00 (operating) + battery cost amortized | Capital cost dominates |
For comparison, utility grid electricity in the US averages roughly $0.16/kWh — substantially cheaper than any generator. Generators are emergency or off-grid solutions, not economical primary power sources for households.
The dual-fuel solution
For most home-backup buyers, dual-fuel (gasoline + propane) generators have become the default for good reason: you get the wattage and cold-weather starting of gasoline plus the indefinite storage of propane. Run on propane for routine exercise runs and short outages; switch to gasoline if extended use depletes propane supply. The dual-fuel premium over gasoline-only is modest ($150–300), and the operational flexibility is worth it.
Tri-fuel (gas + propane + natural gas) units add NG capability for standby-style operation where service is available. Often the same units sold as dual-fuel with an additional NG conversion kit.
The right choice by use case
- Camping, tailgating, jobsite: Gasoline-only inverter — lowest weight, easiest refueling.
- Home backup, moderate outages (2–3 days): Dual-fuel 6,500–9,500W — flexibility and storage life.
- Home backup, frequent or extended outages: Dual-fuel + larger propane tank (100+ gallon), or whole-house standby on natural gas.
- Off-grid or contractor (1000+ hours/year): Diesel, for durability and fuel efficiency.
- Solar/battery + small fuel generator: Best-of-both-worlds for resilience-minded homeowners — solar handles 80% of normal use, fuel generator covers extended outages.
Match the fuel to how you'll actually use the generator, not to a hypothetical scenario.
Frequently Asked Questions
Which fuel is cheapest per kilowatt-hour for a generator?
Natural gas is cheapest where service is available, at roughly $0.08–0.15 per kWh produced. Gasoline, propane, and diesel all land in the $0.30–0.55 range depending on local fuel prices. Utility grid electricity averages $0.16/kWh, so generators are not economical primary power — they're emergency or off-grid solutions.
How long does propane last in storage compared to gasoline?
Propane stores indefinitely with no degradation. A 20-pound BBQ tank you fill today will still run a generator five years from now. Gasoline, by contrast, starts to degrade in 30 days untreated, or 12–24 months with stabilizer. This storage life difference is the primary reason home-backup buyers prefer propane or dual-fuel.
Why do generators produce less wattage on propane than on gasoline?
Propane is less energy-dense per pound than gasoline, and the burn characteristics inside a small engine are slightly different. The result is typically 10–15% lower power output on propane than gasoline for the same generator. A 7,500W dual-fuel generator delivers about 6,375–6,750W on propane. Size accordingly if propane will be your primary fuel.
Is diesel worth it for a portable generator?
Only if you'll run the generator hundreds of hours per year — contractors, off-grid users, mobile commercial operations. Diesel portables cost 3–5x as much as equivalent gasoline units, and the durability and fuel-efficiency advantages only pay back at high annual hours. For typical home-backup users running 20–50 hours per year, gasoline or dual-fuel is the better economic match.
Can I convert my gasoline-only generator to run on propane?
Conversion kits are available for many popular generator models (Hutch Mountain, US Carburetion, and others sell these). Quality varies. Conversion typically allows propane-only or gas/propane switching with a manual lever. Done correctly, conversions work, but they may void the manufacturer's warranty and require careful jet sizing for safe operation. If propane capability matters, buying a factory dual-fuel unit is usually the better path.