Energy shares have held up in the face of a potentially massive political shift to the left in Alberta even as some executives and analysts warn of surging industry costs.

Albertans vote on Tuesday after an extraordinary campaign in which the left-wing New Democrats under leader Rachel Notley piled up big leads in opinion polls, suggesting the first change in government in more than four decades. Ms. Notley wants Alberta corporations to pay more to finance public services.

Jim Prentice's Progressive Conservatives ran on a deficit budget that spared the oil patch new taxes or higher royalties, hoping for voters to shoulder more costs. They have fallen to third place in many surveys, behind the Wildrose Party.

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Despite what could be drastic change in Canada's right-wing bastion, the Toronto Stock Exchange's largely Alberta-based energy group has climbed more than 2 per cent since the election was called on April 7.

In that time, oil markets have played in favour of the sector, rising 9 per cent.

That, and skepticism about opinion polls because of past inaccuracies, has likely prompted investors to hold their fire, said Martin Pelletier, portfolio manager and co-founder of Calgary-based TriVest Wealth Counsel Ltd.

"They don't believe the polls. Even the PCs, internally, don't believe the polls," Mr. Pelletier said. Still, an NDP victory would eventually be negative for oil and gas stocks, he added.

A big reason is the potential for higher royalty rates, against which oil executives have railed as they released results showing the ravages of the oil-price crash in the first quarter.

Last week, Steve Williams, chief executive of Suncor Energy Inc., steered clear of commenting on "hypothetical" royalty reviews, but said the company seeks "predictability" when weighing investments.

"We have to position ourselves to be able to work with all governments, so whatever comes our way, we'll be working with them," he said.

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Royalties are the most politically volatile energy issue since former PC premier Ed Stelmach raised rates in the past decade as oil and natural gas prices fell due to the global financial crisis.

At the time, companies large and small threatened to squelch investment. Shares of producers with operations in the province were hit as some major investors issued sharp rebukes, some comparing Alberta to Venezuela under socialist leader Hugo Chavez.

The PC government, which had expected billions of dollars in additional royalty income from the changes, eventually backtracked.

Ms. Notley's NDP has advocated a new review of the highly complex royalty regime to determine whether Albertans are getting acceptable rent on their resources. The Tories and Wildrose have promised no changes to the royalty structure.

In a report on Monday warning of "unknown investment risk" associated with an NDP victory, AltaCorp Capital Inc. drew comparisons to the previous royalty review. It predicted a similarly negative impact on stocks, saying investors could look to U.S. alternatives.

"Overall, investors will likely weigh investment decisions on the party's historical messaging that suggests royalty rates should be materially higher, which ultimately will be negative for energy share prices," the brokerage said.

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The NDP has said it would hike the corporate tax rate to 12 per cent from 10 per cent, a move the Tories resisted in their March budget. The New Democrats said companies should pay more to make sure health care and education are not underfunded.

Mr. Prentice had said raising corporate taxes would translate into more job losses in the oil patch, adding to cuts being made in response to the collapse in crude prices. The NDP has pointed out that its rate would put taxes back to levels under former premier Ralph Klein.

The Wildrose Party, on the political right of the PCs, has called for no changes to oil-patch taxes and royalties.

Ms. Notley has also said she would stop government promotion of the Northern Gateway and Keystone XL pipelines, in sharp contrast to Mr. Prentice's plans to keep spending tax dollars to push projects aimed at adding new markets for Alberta's oil, among the highest-cost deposits globally.

"Right now, the energy industry's got more than enough problems," said John Stephenson, president of Stephenson & Co. Capital Management in Toronto. "A government that isn't sensitive to that and sees pockets of cash that can be raided is probably not the right thing for resource development."