Petrol vs Diesel Generator: Which Fits Your Site?
Choose petrol for occasional, short-duration use: a lighter, cheaper generator for backup power, small tools, or a job that only needs a few hours of power at a time.
Choose diesel for regular or all-day use: better fuel efficiency, longer engine life, and lower running cost per hour once you're using it often or for extended periods.
The deciding factor is usually run time and frequency of use, not power output on its own — Riequip sells comparable kVA ratings in both fuel types.
Who this guide is for
Home backup buyers
Want a generator that sits ready for the occasional power cut, without worrying about fuel going stale in storage.
Tradies and contractors
Running power tools for a few hours a day versus running a generator all day on a larger site.
Farmers and site managers
Need generators that run for extended periods, sometimes unattended, with minimal servicing in between.
Decision table
| Factor | Petrol generator | Diesel generator |
|---|---|---|
| Upfront cost | Generally cheaper to buy at the same power rating | Generally more expensive to buy, reflecting a more durable engine |
| Running cost | Higher fuel burn per kWh produced; petrol is typically pricier per litre than diesel | More fuel-efficient per kWh produced, and diesel is typically cheaper per litre |
| Engine lifespan | Shorter service life under heavy or continuous use | Built for higher duty cycles and longer service life, especially in enclosed/silenced models |
| Fuel storage | Degrades faster in storage; needs stabiliser or periodic running if sitting idle for months | Stores for longer without the same carburettor fouling risk |
| Weight and portability | Lighter for a given output; easier to move by hand | Heavier for a given output, particularly in silenced/enclosed canopy models |
| Best suited to | Occasional use, short jobs, home backup, camping and light trade work | Regular or all-day use, standby power, farms, larger sites and industrial/prime power |
What's actually available in each fuel type
Riequip's current range spans both fuel types at comparable outputs, so fuel type is a genuine choice rather than something dictated by power rating alone:
Titan Envirogen inverter range
Portable inverter petrol generators from the 4kW Envirogen 4800i up to the 11kW Envirogen 13000iE, suited to home backup, camping and light trade use.
Genmac Honda-powered range
Honda-engined conventional generators such as the RG7300HAC (7.7kVA) up to the G18000HEO three-phase model (18kVA), for higher petrol-powered output.
Anderson silenced range
Fully enclosed, silenced diesel generators from 5kW up to 7.5kW three-phase, built for continuous or unattended running.
Genmac Yanmar-powered range
Diesel generators such as the RG5000YS (6.1kVA) up to the Urban G15000YS (14.9kVA), for higher duty-cycle farm and trade use.
Kubota-powered range
Silent enclosed canopy diesel generators powered by heavy-duty Kubota engines, in single and three-phase, built for standby and prime power on farms, businesses and construction sites.
Cummins-powered range
Silent enclosed canopy diesel generators powered by Cummins engines, spanning light commercial standby through to larger prime power installations.
As one comparison at a similar output: Riequip's Anderson 5kW silenced diesel generator is priced higher upfront than an equivalent petrol conventional generator, reflecting the more durable engine and silenced enclosure built for regular or standby use. At the higher end of the diesel range, the Cummins-powered and Kubota-powered silent enclosed models are built specifically for standby and prime power use rather than portable job-site work, reflecting how far the diesel category extends beyond the portable generators covered above. For a full breakdown of every generator category Riequip carries, including inverter, standby, PTO and trailer-mounted options, see Generators: The Full Range Explained.
Why this recommendation fits
Diesel engines are built to compress fuel at a higher ratio than petrol engines, which makes them inherently more fuel-efficient and better suited to sustained load, at the cost of a heavier, more expensive engine. Petrol engines are lighter and cheaper to manufacture, which keeps purchase price down, but they wear faster under continuous heavy use and petrol itself degrades in storage over a period of months.
That's why the choice tracks run time and frequency more closely than it tracks raw power output: a generator that runs for two or three hours a handful of times a year has very different requirements to one running eight hours a day on a job site, even if both need a similar kVA rating.
When not to choose based on fuel type alone
Fuel type is only one part of the decision. If you need whisper-quiet, clean sine wave power for sensitive electronics or noise-restricted areas, an inverter generator (available in petrol) may matter more than fuel type. If you already run a suitable tractor, a PTO generator avoids the fuel-type question altogether by drawing power from the tractor's own engine. See Generator vs Inverter Generator for that comparison.
Limitations and alternatives
- Running cost estimates are indicative. Actual fuel burn depends on load, generator efficiency and current fuel prices, which change over time. Use the figures in this guide as a starting point, not an exact quote.
- Three-phase requirements may narrow your options in either fuel type; confirm what your equipment needs before choosing a model.
- PTO generators are a diesel-adjacent alternative worth considering if a suitable tractor is already available on-site, since they have no engine of their own to fuel or service separately.
Supporting evidence
- Petrol and diesel generator models, outputs and pricing referenced in this guide are drawn from Riequip's current generator range at riequip.co.nz/collections/generators, with standby and prime power models drawn from riequip.co.nz/collections/cummins-diesel-powered-generators.
- Confirm exact requirements for your situation with the generator calculator or a Riequip specialist before purchasing, as prices and specifications are subject to change.
Frequently asked questions
- Is a diesel generator cheaper to run than a petrol generator?
- Generally yes, per hour of runtime. Diesel engines are more fuel-efficient and diesel is typically cheaper per litre than petrol, so a diesel generator usually costs less to run over long or frequent use. Petrol generators cost less to buy upfront, so for occasional or short-duration use the higher running cost of petrol may not outweigh the lower purchase price.
- Which lasts longer, a petrol or diesel generator engine?
- Diesel engines are generally built for longer service life and higher duty cycles than equivalent petrol engines, which is why diesel is the standard choice for standby, industrial and continuous-use generators. Petrol generators are typically built for lighter, intermittent use.
- Can I leave a generator unused for long periods?
- Petrol degrades faster in storage than diesel and can gum up a carburettor if a generator sits unused for months, so petrol generators suit more regular use or need fuel stabiliser and periodic running if stored long-term. Diesel stores for longer without the same carburettor risk, which is one reason diesel is common for standby generators that may sit idle for long stretches between an outage.
- Is a petrol or diesel generator better for a job site?
- It depends on how long and how hard the generator runs each day. For short bursts of power tools, a petrol generator is usually lighter, cheaper and easier to manage. For all-day running, welding, or powering multiple trades on a larger site, diesel's better fuel efficiency and durability under sustained load usually make it the more cost-effective choice.