Quebec's Canadian Automobile Association is raising questions about whether gas retailers are artificially inflating their prices before the weekend.

A recent study by the non-profit group, focused on Montreal, found that there were sharp increases in the price of gas on 17 Fridays in 2015.

The CAA said in a press release that 11 of those surges were "excessive" and "without foundation."

"There was no justification whatsoever as to why the price had gone up," CAA spokesperson Anne-Sophie Hamel told CTV News.

This is the second year in a row that CAA has accused gas retailers of weekend price gouging.

"The trend right now, unfortunately, looks to be bad for consumers," said Concordia University finance professor Lorne Switzer. 

But critics suggest the study overlooks two important factors: price spikes often happen on other days, besides Friday; and there is a lack of competition among Canadian refineries, which leads to higher wholesale gas prices for retailers.

"I see CAA has made no comments about the refinery profits," said Dan McTeague, senior petroleum analyst at

"It should because that's where the big money is being made."

But CAA insists gas stations often raise prices, despite downward-trending indicators like the price of crude oil.

"We hope that the industry can give us more information as to why this is their strategy and why they don't follow the indicators more closely," said Hamel.

However, the study found that Quebec motorists saw prices at the pump last year that were on average 16 per cent lower than in 2014. 

The Canadian Fuels Association told CTV News that it disputes any accusations of collusion, and added that gas prices were down across the country last year largely due to the tumbling value of oil.

With a report from CTV Montreal's Kevin Gallagher