There is no single winner. The better choice between a used diesel and a used petrol car in 2026 depends on how far you drive each year and what you tow. A used diesel makes sense if you cover high annual kilometres, drive mostly on the highway, or tow regularly. A used petrol car is the smarter buy for low-kilometre city driving, short trips, and lower upfront repair risk. This guide breaks down the real costs, reliability, resale value, and 2026 Australian rules so you can pick the right fuel type with confidence. New to buying second-hand? Start with our complete guide to choosing the right used car.
The quick answer: diesel or petrol used car?
Buy a used diesel if you drive more than roughly 20,000-25,000 km a year, do mostly open-road kilometres, or tow a caravan, boat or trailer. Diesels return better fuel economy and produce more low-rpm torque, which suits long highway runs and heavy loads.
Buy a used petrol car if you drive mostly in the city, cover fewer than about 15,000 km a year, take lots of short trips, or want to avoid the higher repair-cost risk that comes with older diesel components like the turbocharger, injectors and diesel particulate filter (DPF).
The deciding factor is your annual kilometres, because that determines whether diesel’s fuel savings ever outweigh its higher purchase price and servicing costs. We cover that breakeven calculation below.
How diesel and petrol engines differ
Compression ignition vs spark ignition
A petrol engine uses spark ignition: a spark plug lights a compressed mix of petrol and air. A diesel engine uses compression ignition: it squeezes air so tightly that it becomes hot enough to ignite diesel fuel on its own, with no spark plug. Diesel’s higher compression and the higher energy density of diesel fuel are the core reasons it delivers better fuel economy per litre.
Torque, power and towing
Diesel engines produce higher torque at low rpm, which is the pulling force you feel when accelerating from low speed or hauling a load. That is why diesel utes and 4x4s dominate towing. Petrol engines typically rev higher and make their peak power further up the rev range, which can feel livelier in a light city car but less effortless under load.
Refinement and noise
Petrol engines generally run quieter and smoother, especially when cold. Older diesels are noticeably noisier and can clatter at idle, though modern common-rail diesels have closed much of that gap. If cabin refinement matters to you on short commutes, petrol still has the edge.
Is diesel cheaper than petrol in Australia in 2026?
Not at the bowser. As of mid-2026, diesel is more expensive than petrol per litre in most Australian capital cities. Diesel only works out cheaper overall when your fuel savings from better economy outweigh that higher pump price plus diesel’s higher purchase and servicing costs.
Fuel price per litre right now
In Sydney in mid-2026, regular unleaded has been averaging around 187 cents per litre while diesel has averaged around 227 cents per litre. Diesel spiked even harder earlier in the year, peaking near 309 cents per litre in March 2026 before easing. Diesel pricing tends to be more volatile because it tracks global supply, freight demand and seasonal pressures more closely than petrol. The takeaway: you can no longer assume diesel is the cheaper fuel to put in the tank. In 2026 it usually isn’t.
Fuel economy: the L/100km difference
Diesel claws value back through lower fuel consumption. A diesel SUV or ute commonly uses roughly 15-25% less fuel (measured in litres per 100 km) than the equivalent petrol model, and the gap is widest on the highway. A diesel mid-size SUV might sip around 6-7 L/100km on a country run where its petrol twin drinks 8-10 L/100km. That efficiency is diesel’s main financial advantage, and it is the reason high-kilometre drivers still favour it.
The breakeven point: how many kilometres make diesel worth it?
Diesel becomes worth it once your annual kilometres are high enough that the fuel saved covers diesel’s price premium and extra servicing. Because diesel currently costs more per litre, the breakeven sits higher than it did a few years ago, typically around 20,000-25,000 km per year for many SUVs and utes.
To work out your own breakeven, compare the two cars on three numbers: the purchase price difference, the yearly fuel cost of each (your annual km divided by 100, times L/100km, times price per litre), and the difference in servicing costs. If diesel’s yearly savings don’t recover its premium within the time you plan to keep the car, petrol is the cheaper choice.
Running costs and total cost of ownership
Fuel is only part of the picture. Total cost of ownership combines purchase price, fuel, servicing, repairs, insurance, depreciation and registration. On the used market, diesel’s higher fuel efficiency is often offset by higher servicing and repair-cost risk, so you need to weigh all of it.
Servicing and maintenance costs
Used diesels generally cost more to service than petrol cars. They use more oil, often require a specific low-ash diesel oil, and have additional components – turbocharger, EGR valve, DPF and, on newer models, an AdBlue/SCR system – that petrol cars don’t have. Service intervals can be similar, but parts and labour tend to be dearer when something diesel-specific needs attention.
The DPF, AdBlue and repair-cost risk on used diesels
This is the single biggest reason to be cautious with an older diesel. A diesel particulate filter (DPF) traps soot from the exhaust and must periodically burn it off in a process called regeneration, which needs sustained heat from highway-speed driving. A diesel used mainly for short city trips can clog its DPF, and a failed factory DPF can cost many thousands of dollars to replace – sometimes more than the car is worth.
As a rough guide, a healthy DPF lasts around 250,000 km, but problems can appear from 150,000-180,000 km, especially on cars that have lived a stop-start city life. Newer diesels also use AdBlue, a urea solution injected into the exhaust to cut NOx emissions, which you’ll need to top up. Note that removing or deleting a DPF is illegal in Australia and can void insurance and attract fines, so it’s never a legitimate fix. Petrol cars carry none of this DPF/AdBlue overhead, which is a large part of why they’re the lower-risk used buy for city drivers.
How many kilometres should a used diesel have done?
Mileage matters more for diesels than petrols, but how those kilometres were driven matters even more. A diesel with 180,000 highway kilometres and a full service history can be in better health than one with 90,000 short, cold, stop-start city kilometres, because highway running keeps the DPF and engine in their happy zone.
As a practical rule, treat a used diesel approaching 150,000-180,000 km as one where you should budget for a future DPF and turbo, and negotiate harder on price. Always insist on proof of regular servicing and a pre-purchase inspection by a mechanic who knows diesels. For petrol cars, well-maintained examples comfortably pass 200,000 km, and the consequences of high mileage are usually cheaper to fix.
Reliability: which is more reliable used, diesel or petrol?
Petrol cars are generally the lower-risk used buy because they have fewer expensive emissions and forced-induction components to fail. A well-maintained diesel can be extremely durable – the engines themselves are built tough and can outlast petrol units – but the supporting systems (DPF, turbo, injectors, EGR, AdBlue) are where costly used-diesel failures cluster.
Reliability ultimately comes down to maintenance history and use case more than fuel type. A diesel that’s been serviced on time and driven on the open road can be very reliable; a neglected city diesel can become a money pit. If you can’t verify a diesel’s service history, the safer default is petrol.
Resale value and depreciation
Diesel holds its value better in the categories where it makes sense – utes and 4x4s. Demand for diesel dual-cab utes and large off-roaders stays strong in Australia because buyers want towing capacity and touring range, so used diesel examples of vehicles like these typically command a price premium and depreciate more slowly.
For small and mid-size passenger cars, the story flips: petrol (and increasingly hybrid) versions are easier to resell, and the diesel premium is harder to justify. So diesel’s resale advantage is real, but it’s concentrated in the working-vehicle and touring end of the market, not city hatchbacks.
Diesel vs petrol for SUVs, utes and 4x4s (towing)
For towing and serious 4×4 work, diesel is usually the better choice. Its low-rpm torque pulls heavy loads with less strain, its highway fuel economy gives longer touring range between fill-ups, and diesel drivetrains in utes are engineered for sustained hard work. If you tow a caravan, boat or large trailer, a used diesel ute or 4×4 – like a used Ford Ranger or Toyota HiLux – will generally do the job more comfortably than a petrol equivalent.
Petrol SUVs and utes still suit buyers who don’t tow and mostly drive in town, where the diesel’s strengths go unused, and its DPF prefers more highway running than a city life provides. For a school-run family SUV that rarely leaves the suburbs, petrol or hybrid is often the more sensible pick.
Emissions and the environment
Neither fuel is clean, but they pollute differently. Diesels emit less CO2 per kilometre thanks to better fuel efficiency, but they produce more nitrogen oxides (NOx) and fine particulates, which affect local air quality – the very reason DPF and AdBlue systems exist. Petrol engines emit more CO2 per kilometre on average but less NOx and particulate matter. If your priority is lower greenhouse emissions, a modern diesel (or better still a hybrid) can edge out petrol on CO2; if local air quality and simplicity matter more, petrol is cleaner on NOx and particulates.
Are diesel cars being phased out in Australia?
Diesel cars are not banned, but the market is shifting. Australia’s New Vehicle Efficiency Standard (NVES), which applies to new cars supplied from 2025 with its 2026 performance period running through the year, is technology-neutral – it pushes manufacturers toward lower average CO2 across petrol, diesel, hybrid and electric, rather than outlawing any one fuel. Even so, some makers are trimming diesel options: Ford, for example, dropped its 2.0-litre bi-turbo diesel from the Ranger and Everest. For used buyers this is mostly good news – it means plenty of well-supported used diesels remain on the road, but it’s worth factoring long-term parts availability and resale trends into a purchase you plan to keep for many years.
Pros and cons of used diesel vs petrol at a glance
Factor | Used Diesel | Used Petrol |
Fuel economy (L/100km) | Better, especially on the highway | Higher consumption |
Fuel price per litre (2026 AU) | Higher | Lower |
Low-end torque/towing | Stronger | Weaker |
Purchase price | Usually a premium | Lower |
Servicing cost | Higher | Lower |
Major repair risk (used) | DPF, turbo, injectors, AdBlue | Fewer costly extras |
Refinement/noise | Noisier, especially cold | Quieter, smoother |
Best use case | High km, highway, towing | City, short trips, low km |
Resale (utes / 4x4s) | Strong, holds value | Weaker in that class |
CO2 emissions | Lower per km | Higher per km |
NOx / particulates | Higher | Lower |
Which should you buy in 2026?
Choose a used diesel if you: drive 20,000+ km a year, spend most of that on the highway, tow a caravan, boat or trailer, or want a long-touring 4×4 or work ute. Just verify the service history, check the DPF’s health, and budget for diesel-specific repairs as the odometer climbs.
Choose a used petrol car if you: drive mostly in the city, cover under about 15,000 km a year, make lots of short trips, want lower upfront and repair-cost risk, or value a quieter, smoother drive. For many suburban families and commuters, petrol – or a hybrid – is the lower-stress, lower-cost choice in 2026.
Still unsure? Run the breakeven numbers on the two specific cars you’re comparing. If diesel’s fuel savings don’t clearly beat its price premium and servicing costs within your ownership window, petrol wins.
How to inspect a used diesel before buying
- Get a pre-purchase inspection by a mechanic experienced with diesels, specifically checking the DPF, turbo, injectors and EGR.
- Ask for a full service history and proof the correct low-ash diesel oil was used.
- On the test drive, watch for excessive smoke (white smoke can mean unburnt fuel; blue smoke can mean serious DPF or engine wear) and listen for turbo whine or heavy idle clatter.
- Confirm the car does enough highway driving for healthy DPF regeneration; a city-only history is a red flag.
- Run a PPSR check to confirm there’s no money owing and the car isn’t written off.
- For newer diesels, confirm the AdBlue system works, and the warning lights are clear.
