NDP Leader Tom Mulcair wouldn't say Friday how he would alter his fiscal framework if the price of crude continues to sit around $47 a barrel even though some analysts predict this could be a long-term problem, not a short-term symptom.
The NDP, which released its costing document ahead of the economic debate in Calgary, calculated its numbers based on oil at $67 a barrel.
Mulcair said the financial forecast is based on the "best analysis by the best people in Ottawa."
"Our fiscal plan that was put forward was based on the best projections of Canada's finance ministry, backed up by the most recent analysis by the parliamentary budget officer," Mulcair said.
"Our approach ... is sustainable and it is transparent."
Mulcair has continued to call on Liberal Leader Justin Trudeau and Conservative Leader Stephen Harper to put their financial plans on paper.
But the NDP leader has not said how he would pay for his big-ticket promises, such as the multibillion-dollar health-care commitments rolled out this week, if crude prices do not improve.
"I know that the price of commodities goes up and down and it's predictable," Mulcair said.
"That's something Mr. Harper never predicted himself, he never banked on that ... we are being prudent in our approach."
Mulcair went to a Liberal-held riding Friday to announce he plans to work with the provinces on universal prescription drug coverage — but the party is not classifying the promise as a national pharmacare plan.
Speaking in Regina this morning, Mulcair promised $2.6 billion over for four years with the goal of achieving universal access.
The NDP says it will also aim for a 30-per-cent average reduction in the cost of prescription drugs through bulk purchasing programs.
"With a national plan, we can drive down the cost of prescription drugs for Canadians and we can save provinces as much as $3 billion annually," Mulcair said.
"I am a former provincial cabinet minister and I know, I'm confident that this kind of support will help the provinces and the provinces will welcome the direct aid that I am talking about."
Provincial health ministers have been pressuring Ottawa to introduce a full-fledged national pharmacare program.
Mulcair held Friday's event in the riding of Regina-Wascana, which has been held by Liberal Ralph Goodale since 1993.
Goodale, a former finance minister, criticized Mulcair on his costing promises Friday.
"These are glaring errors in Thomas Mulcair's costing," Goodale said in a statement.
"Mulcair is doing the same old political thing: promise a bunch of things you know you can't do. Then after you get elected, say things are much worse than you thought and you can't do what you promised."
The riding is one of two Prairie seats retained by the Grits in 2011.
The NDP wants to improve its electoral fortunes in Saskatchewan, a province where it didn't win a seat in the last election.
Former NDP MP Lorne Nystrom, who served in the Commons for 32 years, said he believes changes to riding boundaries will benefit the party.
"The last campaign we had 33 per cent of the vote in the province and the Liberals had about 10 per cent," Nystrom said.
"They got one seat and we got none and the Conservatives got 13 because of the way the boundaries were drawn ... now, with the new drawing of the boundaries, if we transfer that vote to the new boundaries, we would have three seats just based on status quo."