Why diesel costs more than petrol (2026)

Short answer

Diesel costs more than petrol when the international price of refined diesel is higher than the international price of refined petrol. The ACCC says Australian retail fuel prices are largely set by international benchmark refined fuel prices and the Australian dollar, and each fuel has its own benchmark: Singapore Gasoil with 10 parts per million sulphur for diesel, and Singapore Mogas 95 for petrol. When the Gasoil benchmark sits above Mogas 95, the gap reaches the bowser.

Two fuels, two benchmarks

Both fuels are refined from crude oil, and the ACCC notes their prices tend to follow similar movements over the long term. But the ACCC also says the fuels have their own supply and demand: compared with petrol, diesel also has remote energy generation and industrial uses. Those differences move the two benchmarks apart, and the benchmarks drive retail diesel and retail petrol prices.

A change in an international benchmark takes around two weeks to work through the supply chain to Australian cities, and longer in regional areas, according to the ACCC.

Tax is the same on both

Excise is charged per litre at the same rate on petrol and diesel: 53.7 c/L from 3 August 2026, according to the ATO. Excise is indexed twice a year in line with the consumer price index, and GST is 10% of the pre-GST price, or 1/11 of the price you pay. So a gap between the two fuels comes from the fuel itself, not the tax on it.

What widened the gap in 2022

The ACCC's December quarter 2022 report found average retail diesel at 222.9 c/L, more than 40 c/L above average petrol at 182.7 c/L. It put this down to higher international refined diesel prices after Russia's invasion of Ukraine: reduced diesel supplies from Russia, and from France because of refinery strikes, while northern hemisphere winter heating demand kept diesel prices high (ACCC, 24 March 2023).

Why diesel has no weekly price cycle

In Sydney, Melbourne, Brisbane, Adelaide and Perth, retail petrol prices rise and fall in regular cycles. The ACCC says retail diesel prices do not move in cycles, so the best day to buy petrol does not tell you when to buy diesel. Compare current diesel reports near you instead.

Check today's gap

The chart above shows today's national diesel and Unleaded 91 averages from FuelRadar's reported prices, and how far apart they have been each day. The gap changes with the benchmarks, so check it again before you compare vehicles or plan a trip. The charts on the media page have the same figures with a CSV.

Sources and limits

Benchmarks, price cycles and the 2022 figures are from the ACCC; the excise rate is from the ATO, through FuelRadar's rates file. Today's averages and gap are FuelRadar's reported prices, not a benchmark price. Sources checked 29 September 2026.