Owners of diesel vehicles such as this ute, are paying more for fuel than they should.
Perth diesel buyers are paying 10c a litre more than they should, a competition expert says.
While the wholesale price of diesel is less than that of unleaded petrol in the city at present, diesel users today are paying an average 124.2 cents a litre, according to FuelWatch.
That compares with an unleaded price of 114.2 cents a litre.
Latest available figures from BP, which controls the Kwinana refinery, show the wholesale price of diesel was 1.2 cents less than unleaded petrol on Wednesday.
Elsewhere in WA, the differential is even greater in diesel's favour, yet it is more expensive at the pump to the tune of between five and 16 cents a litre.
The Singapore benchmark price for diesel has also been tracking that for unleaded petrol. Australian prices are set using the Singapore indicator.
Competition expert Frank Zumbo, an associate professor at the University of NSW, said this meant Perth motorists were being gouged to the tune of 10 cents a litre.
The "continued diesel rip off" made it even more necessary that federal competiton minister Chris Bowen gave Petrol Commissioner Joe Dimasi the power to formally monitor diesel prices under the Trade Practices Act, Mr Zumbo said.
This would enable Mr Dimasi to subpoena oil company records regarding diesel pricing.
Mr Dimasi told WAtoday.com.au earlier this month that international factors were driving up the diesel price, but Mr Zumbo said these factors had eased off.
"A lot of diesel in Asia is used in manufacturing, but demand there has dropped significantly," Mr Zumbo said.
