Diesel vs Petrol vs LPG: Comparing Fuel Costs for WA Drivers

When buying a car in Western Australia, the choice of fuel type has long-term financial consequences that are easy to underestimate. Pump prices for petrol, diesel, and LPG can vary significantly, and when combined with differences in fuel economy, the annual running cost difference between a petrol car and a diesel or LPG alternative can run to hundreds or even thousands of dollars. This guide gives WA drivers the numbers they need to make an informed decision.

Current WA fuel prices by type

The following are representative 2025 price ranges for the Perth metropolitan area based on recent FuelWatch data. Prices vary by location, day of week, and station brand:

Fuel type	Typical Perth price range (2025)	Price vs ULP 91
ULP 91 (standard unleaded)	160 – 215 c/L	Baseline
PULP 95	170 – 228 c/L	+8 to +15 c/L
98 RON	178 – 238 c/L	+15 to +28 c/L
Diesel (pump)	175 – 220 c/L	+5 to +25 c/L
LPG	85 – 110 c/L	-70 to -100 c/L

LPG stands out immediately as by far the cheapest fuel per litre. However, LPG vehicles consume more fuel per 100 km than petrol equivalents, and the number of LPG stations in WA is declining. These factors must be weighed alongside the price advantage.

Petrol (ULP and PULP)

Standard ULP 91 petrol remains the most widely available and broadly compatible fuel in Western Australia. With extensive infrastructure across the entire state, a petrol vehicle is never more than a short distance from a refuel opportunity, even in regional areas.

Modern petrol engines have improved fuel economy dramatically over the past decade. A standard four-cylinder petrol engine in a mid-size car now achieves 6 to 10 L/100 km in real-world driving, and smaller turbocharged engines (1.5L and below) can achieve 5.5 to 7.5 L/100 km.

Petrol prices in Perth follow the weekly Tuesday price cycle: Tuesday is consistently the cheapest day to fill up, with prices jumping on Wednesday and gradually falling back through the week. Timing your fill-ups to Tuesday can reduce your average fuel spend meaningfully.

Diesel

Diesel has two key advantages over petrol for high-kilometre WA drivers:

• Fuel economy: Diesel engines are typically 20 to 35% more fuel-efficient than equivalent petrol engines. A diesel SUV achieving 7 L/100 km versus a petrol version at 10 L/100 km represents a significant ongoing saving.
• Torque and towing: Diesel engines produce high torque at low RPM, making them superior for towing, heavy loads, and outback driving across WA's long, undulating roads.

Diesel prices in Perth closely track petrol but typically sit 10 to 20 cents per litre higher than ULP 91. For a vehicle that genuinely achieves 25-30% better economy, the higher per-litre cost is more than offset. For low-kilometre city drivers, the diesel premium is harder to recoup especially given that diesel cars typically cost $2,000 to $5,000 more to purchase than petrol equivalents.

Diesel also requires careful use in city driving conditions. Diesel particulate filters (DPFs) need periodic regeneration via sustained high-speed driving. Urban-only diesel drivers who never take their car on a highway can face expensive DPF replacements. This largely disqualifies diesel as a good choice for drivers in inner Perth who rarely leave the city.

LPG

Liquefied Petroleum Gas (LPG) is the most price-competitive fuel in WA on a per-litre basis, typically costing 85 to 110 cents per litre compared to 175 to 215 cents for ULP 91. However, LPG contains approximately 25% less energy per litre than petrol, so an LPG vehicle consumes roughly 25 to 30% more litres per 100 km than the same engine on petrol.

Adjusted for energy content, the effective fuel cost of LPG (in cents per equivalent litre of energy) is still typically 30 to 45% cheaper than ULP 91. For high-mileage drivers, this translates to thousands of dollars in annual savings.

The main drawbacks of LPG in 2025 are:

• Declining infrastructure: The number of LPG stations in Perth and regional WA has dropped significantly since the 2010s. Trip planning is required to ensure fuelling availability.
• Reduced boot space: The LPG tank typically occupies a significant portion of the boot, which is a practical inconvenience.
• Declining new vehicle support: Very few new vehicles come from the factory with LPG, and the number of qualified LPG conversion workshops is shrinking.

Real cost per 100 km comparison

Using 2025 Perth average prices and real-world fuel consumption data:

Fuel type	Consumption	Avg price	Fuel cost / 100 km
Petrol (ULP 91)	9 L/100 km	187 c/L	$16.83
PULP 95	9 L/100 km	197 c/L	$17.73
Diesel	7 L/100 km	200 c/L	$14.00
LPG	12 L/100 km	95 c/L	$11.40

At these averages, an LPG vehicle costs $5.43 less per 100 km than an equivalent petrol car. Over 20,000 km per year, that is a saving of over $1,086 per year. Diesel saves $2.83 per 100 km versus petrol, or $566 per year at 20,000 km.

Is an LPG conversion worth it in 2025?

A quality LPG conversion for an existing petrol vehicle in Perth costs approximately $2,500 to $4,500 depending on the engine type and installer. Using a saving of $1,086 per year (20,000 km driver), the break-even point is:

Break-even = Conversion cost / Annual saving = $3,500 / $1,086 = approximately 3.2 years

For a driver who plans to keep the vehicle for more than four years and drives above 15,000 km per year, a conversion can still be financially sound. However, the risk of declining LPG station coverage across WA must be factored in. Drivers who regularly travel to regional areas should carefully map their routes before committing to LPG.

Fuel availability across WA

Fuel type	Perth metro	Regional WA (major towns)	Remote WA
ULP 91	Excellent	Excellent	Limited but available
PULP 95	Good	Moderate	Rare
Diesel	Excellent	Excellent	Good (common at roadhouses)
LPG	Declining	Limited	Very rare

Environmental considerations

From a greenhouse gas perspective, LPG emits roughly 15% less CO2 per kilometre than petrol (when accounting for higher consumption). Diesel emits slightly more CO2 per litre than petrol but the economy advantage means total CO2 per km is typically 15 to 25% lower for diesel. Both are still meaningfully higher in emissions than battery electric vehicles, though EV infrastructure in remote WA remains a significant practical barrier.

Which fuel type is right for you?

• City-only driver under 15,000 km/year: Petrol ULP 91 or PULP 95 (as required). Simple, widely available, no DPF risk, lowest purchase price.
• High-mileage driver above 25,000 km/year: Diesel or LPG. The economy advantage repays the higher running costs or conversion investment quickly.
• Towing or 4WD regional travel: Diesel is the clear winner. Torque advantage, excellent fuel availability at WA roadhouses, diesel-specific advantages at altitude in the Kimberley.
• City taxi, Uber, or high-mileage commercial: LPG still makes sense if routes keep you within the Perth metro LPG network.
• Environmental priority: Diesel for maximum efficiency. EV where infrastructure allows (broadly viable in Perth metro and between major South West cities).