The increase from 118.2¢ last week was the steepest out of all capital cities, with the next-highest prices, in Brisbane, moving by just 7.3¢ in the same week, ended March 8.

Prices across the country rose by 4.6¢ a litre in the same period, and were an average of 128.5¢ a litre across the five major cities.

Canberra joined Hobart on Tuesday and Wednesday last week when the pump prices leapt higher, according to CommSec Research.

"The moves represented a lagged response to the higher wholesale price and pump price increases in other capital cities," a CommSec Research report says.

The jump compares to a much smaller, 0.6¢ rise in Canberra prices the week before, ended March 1.

There was a point, however, when ACT prices dropped to the cheapest in the country last week, at 117.6¢ a litre, which brought Canberra closer to the average for capital city prices.

An Australian Competition and Consumer Commission report confirmed in February that, of all major cities, Darwin residents still pay the most for fuel – with these prices staying higher than Hobart and Canberra.

It was revealed on Tuesday that Darwin would be the first city to be studied under the federal government's new petrol monitoring to determine why some regional centres pay much more for fuel.

Local petrol price lobby group ACT Fuel Watch told its many social media supporters that while it was disappointed Canberra had missed out on inclusion in the first study, the group was pleased the probe was going ahead.

Canberra petrol prices were the slowest to fall of all capital cities from July last year to January, according to the ACCC.

Prices did not appear to be dropping significantly this week, with the average price in the ACT sitting at 131.9¢ on Tuesday, and Costco still offering the lowest price, according to the PetrolSpy app.