Record low world oil prices are beginning to flow through to the pump at Australian service stations.

Key points: Unleaded price drops below $1 per litre at service stations in Sydney, Adelaide

Consumer watchdog concerned savings aren't being passed on

Lowest average prices in Adelaide; Hobart the most expensive

The price of unleaded petrol has dipped below $1 per litre at three petrol stations at Blacktown in Sydney's west.

South Australia's Royal Automobile Association has also listed fuel prices below a dollar at three Adelaide service stations.

In Queensland, the RACQ's public policy manager Michael Roth also predicted prices could drop to 99.9 cents with some service stations using the below-dollar price as a "marketing gimmick".

"We're unlikely to see petrol below $1 as an average, as the wholesale price is still sitting above 105 cents a litre and they would be selling at a loss," he said.

The drop in national petrol prices follows pressure from consumer watchdog the Australian Competition and Consumer Commission (ACCC), who were concerned that the low world oil prices were not being passed on to motorists.

Australasian Convenience and Petroleum Marketers Association chief executive Mark McKenzie said the drop is part of the normal price cycle.

"Retailers are basically businesses in their own right, so they'll make margins. What they're basically doing is passing on the lower costs of fuel as it comes through," he said.

"We were all expecting this in terms of the continued downward pressure on global oil.

"What you're actually seeing here is ... world oil prices flow through to the pump and it will continue that we'll actually see the ups and downs that we normally get with the price cycle."

Crude oil prices have slumped 20 per cent this year to about $US28 a barrel. Eight months ago prices were hovering around the $US65 mark.

Loading

According to figures from motoring industry group MotorMouth, the capital city with the lowest unleaded petrol price on Tuesday was Adelaide, which had an average of 104.1 cents.

It was followed by Sydney (108.1), Melbourne (109.1), Brisbane (120.0), Perth (125.0), Darwin (125.1), Canberra (125.8) and Hobart (129.6).

Motorists will have access to the same petrol price information as retailers under a deal brokered by the ACCC last year.

Retailers currently have exclusive access to price moves data from Informed Sources, but that information is expected to be available to consumers for free and to third parties on commercial terms.