Last week's national average price for unleaded petrol fell by 3c to 148.0c, as Sydney, Melbourne, Brisbane and Adelaide all recorded drops of between 4c and 6c.

Melbourne had the lowest average price at 140.7c, while Darwin remained the most expensive capital city at 168.3c.

Canberra prices were down 0.1c to 156.4c a litre, making the gap between Sydney and Canberra now more than 13c per litre - or almost 10 per cent.

Analysis by Commsec economists found wholesales prices fell by 2c and there was scope for petrol prices to fall another 2c or 3c during the coming fortnight.

CommSec chief economist Craig James said retailers could celebrate the falling petrol price, along with more stable conditions on the financial markets and gains in house prices.

"Filling up the car with petrol is the single biggest weekly purchase for many Australian families," Mr James said.

"The 7.5c fall in the petrol price in the past six weeks has put an extra $5 back in Aussie wallets each time they fill up with petrol."

Last month, ACT motorists paid an average of 157.9c for unleaded fuel.

Average petrol prices in the week to Sunday, October 27:

Canberra: down 0.1c at 156.4c

Sydney: down 5.3c to 143.4c

Melbourne: down 6.2c to 140.7c

Brisbane: down 6.5c to 146.7c

Adelaide: up 4.5c to 149.6c

Perth: down 0.5c to 145.9c

Darwin: unchanged at 168.3c

Hobart: down 1.0c to 162.1c