Same tax, different fuel
Diesel and petrol pay the same excise, 53.7c a litre since 3 August 2026, and the same 10% GST. So whatever makes diesel dearer is in the price of the fuel itself, which is set by the international market for refined diesel. Australia imports most of its diesel, mostly from refineries in Asia, so it pays that price plus shipping.
For most of the past two decades diesel cost 2 to 7c a litre more than petrol at wholesale. In 2022 the gap averaged 21.5c. So far in 2026 it is 33.2c.
What sets the gap
A refinery does not choose freely how much petrol and how much diesel it makes from a barrel of crude. Both come out of the same barrel, in proportions that can only be shifted so far. So the relative price of the two is set by demand.
- Diesel runs the economy. Trucks, trains, ships, mines, farms, generators and construction all run on it. When economic activity picks up, diesel demand picks up with it, and it barely falls when the price rises because there is no alternative in the short term.
- Petrol is mostly private cars. Demand is steadier, more sensitive to price, and in some countries already falling as cars become more efficient and electric.
- Winter in the northern hemisphere adds demand for heating oil, which competes with diesel for the same part of the barrel, so diesel often firms in the northern winter.
- Diesel is the product the world is shortest of in a crisis. Russia was one of the world's biggest diesel exporters. When Europe stopped buying it after 2022, it had to find diesel elsewhere, including in Asia, and that competition has kept the gap wider ever since.
When diesel was cheaper
National wholesale diesel averaged less than petrol in 2015, 2016 and 2017, and again in 2021. In each case the world had plenty of diesel. The years 2015 to 2017 followed the oil price collapse of late 2014 and a slowdown in global industry, and in 2021 freight and travel were still recovering from the pandemic. In January 2016 national wholesale diesel fell to 88.2c a litre, its lowest since 2004, while petrol was 101.9c.
The first blowout in 2022
When Russia invaded Ukraine in February 2022, diesel was hit harder than crude because Russia exported so much refined diesel. Australian wholesale diesel averaged 191.5c across 2022 against 170.0c for petrol. The gap took more than two years to narrow, to 2.6c across 2024.
A second, bigger one in 2026
The disruption around the Strait of Hormuz from late February 2026 hit diesel harder still. These are the national wholesale monthly averages, in cents a litre.
| Month | Petrol | Diesel | Diesel premium |
|---|---|---|---|
| February 2026 | 153.4 | 162.9 | 9.5 |
| March | 210.4 | 249.4 | 39.0 |
| April | 193.7 | 271.6 | 77.9 |
| May | 177.8 | 211.4 | 33.6 |
| June | 157.0 | 179.4 | 22.4 |
| July | 169.7 | 198.3 | 28.6 |
| August | 195.9 | 239.5 | 43.5 |
| September | 216.7 | 256.2 | 39.5 |
Australian Institute of Petroleum terminal gate prices, including excise and GST. April and May include the excise cut, which applied equally to both fuels and so does not affect the premium.
April's 77.9c premium is the widest monthly gap in our data back to 2004. On 9 April national wholesale diesel reached 325.9c, its record. The excise cut that took effect on 1 April lowered both fuels by the same amount, which is why it barely registered for diesel buyers. The wholesale data shows the cut was overtaken within a week.
What it means if you drive a diesel
- Diesel does not follow the petrol price cycle, so timing your fill by the cycle does not help. Comparing servos does, and diesel prices vary more between truck stops and car-focused servos than petrol does.
- A diesel car typically uses less fuel than an equivalent petrol car, which offsets part of a normal premium. At a 40c premium, that advantage is mostly gone. Put both into the calculator to see what it does to your weekly cost.
- If you run a business, the fuel tax credit lets you claim back most of the excise on diesel used off public roads, and part of it for heavy vehicles on road. That is worth more than any discount.
Where these figures come from
Wholesale prices are the terminal gate prices published each weekday by the Australian Institute of Petroleum, which we hold back to 2004. The national figure is AIP's own average where it has published one, and our weighted calculation in between, which matches AIP's to within 0.1c. Oil and currency prices are delayed market closes. Excise rates are the ATO's. We check every figure against that data before publishing and correct mistakes in the update log. Spotted one? Email hello@thepetrolprice.com.