Canberrra's average fuel prices of 120.8 cents a litre this week sat below the national metropolitan average of 124.9 cents a litre and the capital city average of 123.7 cents a litre.

The average cost of unleaded petrol in Canberra fell sharply when travel restrictions and gathering limits were first implemented, but retailers took longer in the ACT to pass on savings than in other parts of the country.

During the week ending December 1 last year, the average price of unleaded petrol in the ACT was 147.7 cents a litre, and stayed above 140 cents until the week ending March 29, according to statistics published by the Australian Institute of Petroleum.

The average price fell to a low of 101.3 cents a litre in the week ending May 10, before prices slowly climbed until July, reaching a high of 122.9 cents a litre on August 2. The price has stayed around 120 cents a litre in the weeks since.

Although the average price in Sydney fell to 92 cents a litre in the week ending May 3, the city's price cycle means the average price moves quickly above and then below the average price in Canberra.

Melbourne's prices did not drop as low as prices in Canberra, despite the extended lock-down period when Victoria tackled its second coronavirus wave and movement was restricted to within a 5 kilometre radius. However, prices have remained consistently lower in Melbourne than Canberra, where the average price was 116.7 cents a litre last week.

In April, the ACT government threatened legislative action against retailers whose petrol prices remained high while the oil price crashed and petrol prices fell in other parts of the country.

At the time, Australian Competition and Consumer Commission chairman Rod Sims warned retailers not to use the pandemic "to further increase profits".

"[In] Hobart, Canberra and Darwin as well as many regional locations, retail prices have been much slower to come down and the extent of the falls has varied widely," Mr Sims said.

"We have previously found that the lack of vigorous and effective competition in some regional locations was a major reason for higher prices in those locations."

A seven-month inquiry conducted by a cross-party Legislative Assembly committee last year found the cost of fuel was largely dependent on external factors, including crude oil prices and exchange rates, but Canberra's lack of independent outlets, no petrol stations on main road and higher business costs contributed to higher fuel prices.

The committee recommended forcing service stations to provide their prices to a government-regulated fuel monitoring website, which the NRMA said would be a "much-needed wake-up call" to the industry.