Despite being just three hours from Sydney, Canberrans were paying seven more cents a litre above five of the country's capital cities in 2013−14.

In its seventh report, the ACCC also found motorists across the country were hit with historically high prices for filling up at the bowser this year.

The ACCC said the average retail price for regular unleaded petrol in the country's five largest cities was 150.6 cents per litre in the 2013-14 financial year, with Canberrans paying an average 157.4 cents.

150.6 cents represents a 9.3 cent increase on the previous year, and the third-highest average price on record in real terms.

"This was primarily driven by the international oil price and the Australian-US dollar exchange rate," ACCC chairman Rod Sims said on Wednesday.

Prices in the three smaller capital cities of Darwin, Hobart and Canberra are always higher than in the five largest cities, and regular unleaded prices in Darwin again topped the pack at 170.4 cents a litre.

But these cities, along with most regional centres, are also immune from price cycles that force Melbournites and Sydneysiders into strategic filling up habits.

In other fuels in the capital, the annual average diesel price in Canberra was 161.8 cents a litre, with LPG at 85.8 cents and E10 at 155.6 cents.

Up in Sydney, regular unleaded petrol averaged 149.8 a litre, with diesel at 156.6 cents, LPG at 81.5 cents and E10 at 148.4 cents.

In good news for motorists, Mr Sims said retail petrol prices and international refined fuel prices had both dropped by about 20 cents per litre since July.

"As the international price is such a large component of the retail price, this should be a welcome relief for motorists," he said.

"The international price of refined petrol made up 54 per cent of the average price consumers were paying at the pump, while taxes made up 34 per cent."

More relief should be in store for motorists following the slump in global oil price to as low as $US63.72 a barrel this week.