"On the one hand, the (price) of a barrel of crude oil drops, on the other side, gasoline increases," he said while campaigning in the Laurentians north of Montreal.
"Everyone knows there's something that's not working."
The Bloc leader said the falling Canadian dollar doesn't explain everything.
"You just have to look at the refining margins to see where the problem is," he said, referring to the difference between the wholesale value of the oil products a refinery makes and the value of the crude oil used to make them.
Duceppe urged the Competition Bureau to look at the practices of large oil companies, which he accused of gouging consumers.
The Bloc leader also called on federal leaders Justin Trudeau, Tom Mulcair and Stephen Harper to commit to setting up a parliamentary committee on the question of gas prices as soon as the Commons resumes after the Oct. 19 election.
"Up until now, the federal parties seem to be have been more concerned with the oil companies instead of people," he said.
"We need answers. I invite my opponents to stand up for the middle class ahead of the oil companies for once."
Duceppe also got a "thanks, but no thanks" from Quebec's other sovereigntist party on Tuesday.
While the Bloc can count on the support of the Parti Quebecois, its provincial counterpart, it can forget about Quebec solidaire, which has three seats in the 125-member national assembly.
"Quebec solidaire is not going to declare its support for one or the other parties, because there is no one who actually represents the ideas of Quebec solidaire on the federal scene," party spokesman Nicolas Levesque said.
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