Canberrans have enjoyed one of their best years for competitive petrol prices, with the arrival of Costco and comparison tool Fuel Watch credited with slashing the cost divide with Sydney.
Motorist advocates have predicted the sustained competition created by last year's shake up will continue, even though this week's sub-$1 per litre prices at three outlets may not.
NRMA ACT and NSW South Coast board member Kate Lundy said the introduction of the Costco fuel station, which opened in December 2014, and ACT Fuel Watch online a month later led to ongoing savings.
"Before Costco's opening, ACT motorists were paying on average 9.5 cents more per litre of petrol than in Sydney, but now they're paying about 3.4 cents more [2015 daily average], which means prices are heading in a positive direction," she said
ACT Fuel Watch co-founder Benjamin Ling said Costco initially affected the prices within a very narrow circumference of its Majura Park base, and the attention drawn to this by the Fuel Watch Facebook page (and now website) widened the area of influence.
Across the first three months of 2015 average Canberra prices had matched those in Sydney, he said, and the recent arrival of Metro Petroleum in Fyshwick and Queanbeyan had helped maintain the more competitive prices.
Mr Ling, a full-time real estate agent with Ray White Belconnen, said Canberra regular unleaded prices were now around 8c more than Sydney according to Petrol Spy, whose data Fuel Watch uses, but Canberra motorists could still have saved an average $1300 last year compared to 2014.
Assuming a weekly fill of a 60-litre tank, the $25 weekly saving would appear to be at the higher end of estimates, but is feasible given the difference between Canberra's cheapest and most expensive base unleaded petrol on Friday was still 36c.
"Prices will continue to go down, until a mid-year resurgence to the new normal which is probably in the mid 120s," he said.
Mr Ling said there was "absolutely nothing wrong" with the way petrol stations in the ACT priced, as they were never making more than 1 or 2c/L profit.
But Ms Lundy said Canberrans were still being ripped off as there was no reason they should pay more than Sydney motorists, given inconsistencies in arguments about transport costs.
She said further city-wide savings would occur only when independent petrol providers built more service stations, and called on the ACT government to continually look at opportunities for new sites to be released.
Costco refused to provide any membership or ACT financial figures, but said Canberrans had embraced the store since its warehouse opening in 2011 and membership continued to be "very strong".
The American discounter giant's Australian arm, which has a flat $60 membership, increased revenue by 50 per cent in the year to August 31, up to $1.32 billion, as sales grew at existing stores and two new stores opened. Its pre-tax profit was $22.7 million.