Ontario's governing Liberals have been handed a confusing and changing series of estimates on the costs of scrapping a gas plant in Oakville, Ont., which is why Premier Kathleen Wynne wants to see what the auditor general concludes in a report due later this year.

A legislative committee is in the midst of probing the cancellation of a pair of gas plants west of Toronto, which appear to have each cost tens of millions of dollars more than what the government had previously claimed.

Earlier this month, Ontario Auditor General Jim McCarter reported that the decision to halt development of a Mississauga, Ont., gas plant two years ago will cost $275 million when all is said and done — a figure that was some $85 million more than the Liberals had been admitting.

The auditor general is still investigating the costs involved with cancelling a similar plant in Oakville, which Ontario Power Authority CEO Colin Andersen testified Tuesday could be as high as $310 million.

Hours later, Wynne voluntarily testified before the committee, where she took questions about her knowledge of and involvement in the decisions to kill the Oakville and Mississauga gas plants.

The premier was also asked why her government had been referring to a $40-million cost in association with the Oakville plant.

"Whenever I have stood and used a number, that has been the number that I have understood to be the real number," she told the committee on Tuesday afternoon

"I believe the complexity and the fact that the OPA numbers keep changing justifies my decision to call in the auditor. We need to wait for the auditor general's report."

Wynne also testified that she was not involved in the decisions to relocate either plant, telling the committee that she learned about the Mississauga decision through the media.

Opposition members remained frustrated with Wynne and her government following her testimony on Tuesday. Both the Progressive Conservatives and New Democrats wanted to know why the Liberals had not previously admitted that the Oakville costs would exceed $40 million.

"I think that why she was so evasive in coming clean with a number was she knows her government's been lying all along about it and didn't want to put anybody else on the spot," said PC energy critic Vic Fedeli.

"Seven times we've heard from witnesses that the government knew the number was higher than $40 million, and the fact that she wouldn't acknowledge it just continues the coverup."

NDP committee member Taras Natyshak said he felt the premier was "evasive" when answering questions.

"We pressed her hard, giving her the space to acknowledge that all along they knew that there was no way that the cancellation of the plant would be limited to a $40 million cost," he said.

Continuing controversy

The controversy over the gas plant cancellations has raged for months, with opposition members continually questioning the government about the process surrounding those decisions and the costs.

The Liberal government released several batches of documents relating to the gas plants, more than once having to release more after finding that some had not been released.

More recently, the Progressive Conservatives moved a non-confidence motion that relates to the cancelled gas plants, but it is unlikely to go forward as the Liberals will not call it for a vote.

The premier has said that the upcoming budget, which is due to be tabled on Thursday, will be an opportunity for the opposition parties to vote on a confidence matter.

The minority Liberals need the support of at least one opposition party in order for the budget to pass and for the government to survive.

At the moment, the Liberals hold 51 seats in the legislature, while the Progressive Conservatives hold 36 and the New Democrats 18. Two seats are currently vacant, due to the resignations of two Liberal cabinet ministers in recent months.

The Progressive Conservatives have vowed to vote against the Liberals' pending budget.

The CBC's Mike Crawley reported that a vote on the budget will likely take place between one and three weeks after it is tabled on Thursday.

Crawley said the Liberals appear to be willing to provide a budget that will satisfy the New Democrats.

But it remains unclear how the gas-plant issue may factor into an NDP decision as to whether or not the party can support the government further.

"The key question is how can the NDP continue to prop up a government when they have not been fully truthful with the people of Ontario about the massive cost of these gas plants?" Crawley said.

"That's the question we’re going to really have to watch for in the next few weeks."

With files from The Canadian Press