Canberra petrol prices fell 0.4c a litre last week, but are still 16.7c more expensive than in Sydney.
Figures issued by the Australian Institute of Petroleum found the average pump price in the nation's capital was 149.8c a litre last week, well above $1.32-$1.33 in Sydney, Melbourne and Adelaide, and above the $1.45 regional average.
CommSec chief economist Craig James said prices were likely on their way up again, and predicted a 4c a litre increase over the coming fortnight.
"The good news is that the national average petrol price is at 22-week lows and unleaded petrol has been selling below the wholesale cost in many cities for the past week," he said.
"The bad news is that it can’t last and unleaded petrol prices could lift up to 4 cents a litre over the next fortnight as recent increases in wholesale prices flow through to pump prices.
"The interesting development across a number of capital cities in recent months has been the change in the petrol discounting cycle.
"While Perth has stuck to a weekly discounting cycle, in Sydney, Melbourne, Adelaide and Brisbane, it can take up to two weeks for prices to fall from cyclical highs to the cyclical lows. And that change has made it more difficult in lining up regional, wholesale and retail prices."