Gas vs Propane vs Diesel Generators: Fuel Compared
The fuel decides how long your generator can run, how you store it, what it costs per hour and how much power you get. This guide compares gasoline, propane, natural gas and diesel using stated figures from the manufacturers in our generator comparison tool, retrieved on 2 November 2026. For storage and shelf life, see our longer guide to generator fuels.
At a glance
| Fuel | Where you find it | Strength | Trade-off |
|---|---|---|---|
| Gasoline | Portable and inverter generators, RV units | Easy to buy and carry | Degrades in storage, so it needs stabiliser and rotation |
| Propane | Dual-fuel portables and home standby units | Stores for long periods in a tank | Lower output than gasoline on the same engine |
| Natural gas | Home standby units | Continuous supply from a utility line | Needs a gas line; lowest rated output on the units we compare |
| Diesel | Commercial and industrial sets | Efficient at load and built for long runs | Larger, heavier, and usually a dealer purchase |
What the manufacturers state
The table compares one gasoline RV generator, one commercial diesel and one home standby unit that runs on propane and natural gas. They are very different machines, so read it for the fuel figures, not for a winner.
| Specification | Cummins OnanRV QG 4000 (built-in RV generator)Portable | GeneracSD020 20 kW Industrial DieselCommercial and industrial | GeneracGuardian 22 kW Air-Cooled Home StandbyHome standby |
|---|---|---|---|
| Price and ownership cost | |||
| Listed price (USD, estimate) | Not publishedInstalled by RV makers and dealers; not priced on the spec sheet | Not publishedQuote through a Generac dealer | Not publishedGenerac does not list a price on the spec sheet; installed cost varies by dealer |
| Price per rated watt (derived) | n/a | n/a | n/a |
| Warranty | Limited: 2 years on nearly everything but routine maintenance, plus parts and labor on major parts in year 3 | 2-year limited (standby rated); 5, 7 and 10-year extended options | 5-year limited |
| Maintenance | Not stated | Not stated | Oil change interval up to 2 years or 200 hours, per the spec sheet |
| Oil capacity | 1.6 qt (1.5 L) | 9.3 qt (10.6 L) | 1.9 qt including filter |
| Power | |||
| Rated output by fuel |
|
|
|
| Starting or surge watts | Not stated | – | – |
| Fuel types | Gasoline | Diesel | Propane / Natural gas |
| Engine | Cummins Onan E095H, 4-cycle OHV single cylinder | Perkins 4-cylinder in-line, 2.2 L, 1,800 rpm, 32 hp at rated kW | Generac G-Force 1000 Series, 2-cylinder |
| Displacement (cc) | 304 cc | 2,220 cc | 999 cc |
| Runtime, fuel use and running cost | |||
| Fuel tank (gal) | Not stated | – | – |
| Runtime on a tank, as stated | Not stated | – | – |
| Fuel use, as stated |
|
|
|
| Fuel per kWh (derived) | 0.25 galgasoline at 50% load, from stated fuel use | 0.106 galdiesel at 50% load, from stated fuel use | n/a |
| Fuel cost per kWh at your price (derived) | n/a | ||
| Fuel cost per hour at that load (derived) | n/a | ||
| Size and comfort | |||
| Weight (lb) | 172 lb | 1,456 to 1,641 (open set, no tank) lb | 445 to 466 lb |
| Dimensions | 30.0 x 19.7 x 14.4 in | 76.0 x 37.4 x 44.8 in (open set, no tank) | 48 x 25 x 29 in |
| Noise (as stated) | 68 dB(A) at 10 ft, half load | Not stated on the spec sheet (enclosure options listed) | 67 dB(A) at 23 ft, normal load; 55 to 57 dB(A) in Quiet-Test exercise mode |
| Starting method | Remote start from the RV | Automatic (12 V solenoid starter) | Automatic (on utility failure) |
| Features | |||
| Inverter output | No | No | No |
| Total harmonic distortion | Not stated | Under 5% (three-phase models) | Less than 5% |
| Automatic voltage regulation (AVR) | Not stated | Yes | Yes |
| CO sensor shutdown | Not stated | – | – |
| Transfer switch ready | Not stated | Yes | Yes |
| Transfer switch detail | – | Sold separately | 200 amp service-rated automatic transfer switch available |
| Parallel capable | Not stated | – | – |
| Outlets and connections | Hard-wired to the RV; 120 V | Hard-wired; single or three phase configurations | Hard-wired to the home; 120/240 V single phase |
| Fit | |||
| Suited to | RV and travel trailer | Commercial, Industrial | Whole-house power, Home backup |
| Also worth knowing | Mounts in an RV compartment and draws from the vehicle fuel system | Standby rating 20 kW / 25 kVA at 60 Hz; prime rating 18 kW; frequency regulation plus or minus 0.5%; weather-protected and sound-attenuated enclosures optional | Wi-Fi monitoring standard; listed for installation as close as 18 in to a structure; enclosure rated for winds to 150 mph |
| Honest take | |||
| Advantages |
|
|
|
| Drawbacks |
|
|
|
| Source | |||
| Where the figures come from | Cummins Onan RV QG 4000 spec sheet (PDF)Retrieved 2026-11-02 | Generac SD020 spec sheet (PDF)Retrieved 2026-11-02 | Generac Guardian 20/22/24 kW spec sheet (PDF)Retrieved 2026-11-02 |
Power you lose on propane
Dual-fuel generators make less power on propane. The Champion 201050 is rated at 3,000 running watts on gasoline and 2,700 on propane. The Westinghouse WGen9500DF is rated at 9,500 W on gasoline and 8,500 W on propane, and the Westinghouse iGen5000DF at 3,900 W on gasoline and 3,500 W on propane. Size your generator for the lower propane figure if you plan to rely on it. The generator size calculator helps.
Fuel use compared
These figures are derived by dividing each maker’s stated fuel use at full load by the rated output. They are rough guides, because a generator’s efficiency changes with load and the machines differ in size and design.
| Generator | Stated fuel use at full load | Rated output | Derived use per kWh |
|---|---|---|---|
| Cummins Onan RV QG 4000 (gasoline) | 0.7 gal/h | 4,000 W | about 0.175 gal |
| Generac SD020 (diesel) | 1.68 gal/h | 20,000 W standby | about 0.084 gal |
| Generac Guardian 22 kW (propane) | 3.90 gal/h (142 cfh) | 22,000 W on propane | about 0.177 gal |
| Kohler 20RESC(L) (propane) | 136 cfh | 20,000 W on propane | about 6.8 cu ft |
| Kohler 20RESC(L) (natural gas) | 281 cfh | 18,000 W on natural gas | about 15.6 cu ft |
| Generac Guardian 22 kW (natural gas) | 306 to 327 cfh | 19,500 W on natural gas | about 15.7 to 16.8 cu ft |
On these numbers, the 20 kW diesel uses about half the volume per kilowatt-hour of the gasoline RV unit. A gallon of diesel also holds more energy than a gallon of propane, so volumes are not directly comparable across fuels. To turn gallons into dollars, enter your local prices in the comparison tool or use the fuel consumption calculator and the generator cost calculator.
Which fuel for which job
- Camping, tailgating and short outages: gasoline, or a dual-fuel inverter if you want a storable backup fuel.
- Home backup with a portable: dual fuel, so you can run propane if gasoline is scarce after a storm.
- Whole-house standby: natural gas if you have a utility line, propane if you do not.
- Businesses, farms and long runs: diesel, bought through a dealer who can size, install and service it.
- No fumes allowed, or a very short outage: a battery power station, such as the EcoFlow DELTA 2 in our database, which has no fuel at all.
Safety
Every fuel-burning generator makes carbon monoxide. Run portables outdoors and far from openings, whatever fuel they use. Our safe generator use guide covers placement and electronics.
What we could not verify
The Cummins sheet is an older revision (A-1399n, June 2011), and Kohler’s is dated January 2019. Neither Generac nor Kohler publishes a price on these sheets. Per-kWh figures are our arithmetic and are labelled as derived.
Frequently asked questions
Is propane cheaper than gasoline for a generator?
It depends on local prices and on the load, because propane gives lower output and different fuel use. Enter your own prices and the stated fuel use into the cost calculator to compare.
Does propane last longer in storage?
Propane stored in a sealed tank does not degrade the way gasoline does, which is why many owners keep a tank on hand for emergencies. Gasoline should be stabilised and rotated.
Why are diesel generators used commercially?
Diesel sets are built for long run times and heavy loads, and the 20 kW unit we list states 1.68 gal/h at full load. They are also larger and heavier, and they are bought and installed through a dealer.
