TORONTO -- Ontario's opposition cried "coverup" Thursday after the government announced dozens more documents had been unearthed on two cancelled gas plants, months after the Liberals repeatedly insisted they had all been released.

"We're sickened by this, that's all I can tell you is my stomach feels sick over this, that this has happened in our province," said Progressive Conservative energy critic Vic Fedeli. "We've said all along there are documents that are being covered up."

It was actually the third batch of gas plant documents and the second time the Liberals have been forced to admit they were wrong when they claimed to have publicly released all the relevant data ordered by a legislative committee.

"I want to know from this premier why anybody in Ontario should have any trust whatsoever in any Liberal in this province," demanded NDP Leader Andrea Horwath.

"The people of this province deserve the answers to why these documents have been withheld from the view of the members of this legislature ... for months and months and months."

The government was sincere when it told the legislature several times last fall that all the documents had been released, said Energy Minister Bob Chiarelli.

"We took the initiative when we found out about these documents to release them of our own volition," said Chiarelli.

"That should be evidence of our willingness to be open and transparent, that when we found out there were more documents they were immediately made public."

The Tories and NDP have said for months they were convinced the Liberals were still hiding documents on the cancellations of the energy projects in Mississauga and Oakville, which cost taxpayers at least $230 million.

"The bottom line is that the decisions were made by this government in order to save Liberal seats in the last election," said Horwath.

"They spent billions of dollars -- likely, possibly, we don't know yet, because we don't have the documents -- on making sure that those Liberal seats were saved."

The government did not explain Thursday why it continued to insist all the gas plant documents had been released after the Ontario Power Authority told the Energy Ministry last November that it was still searching and there would "likely" be more uncovered.

"This is an ongoing process and it's very complicated," Premier Kathleen Wynne told the legislature.

"It's disappointing that we didn't know about it, but we want all of that information to be out in the public."

The NDP accused the Liberals of deliberately trying to cover up the documents.

"This has been an ongoing process of obfuscation of the facts by this government, that's what the ongoing process has been," said a fired-up Horwath.

Horwath complained that the Liberals "acted all indignant" Wednesday after the opposition parties combined to revive a contempt of parliament motion over the "vile scandal" surrounding the release of the gas plant documents.

"They accused us of being mean-spirited," she said.

"Well, I accuse them of being disingenuous."

There was still no sign of any documents related to the gas plants from the premier's office or the ministry of energy, even though more than 56,000 pages have already been released, said the Conservatives.

"If they're going to give us 600 (new) pages when we have 3,000 that are whited out that I presented in this house, we know they're not telling us the full story again," said Fedeli. "It's absolutely sickening."

Asked Thursday whether there were any more documents, Chiarelli said they had all been released -- as far as he knew.

Last September, the Liberals told the legislature that all the documents had been released with 36,000 pages, only to find another 20,000 pages a month later.

OPA chairman Jim Hinds issued an apology Thursday and said it was "inadvertent" that the newly found documents -- which included emails, letters and meeting appointments -- were overlooked in the first two searches.

"I don't think cover up is the right way to describe it. We messed up some search terms," said Hinds.

"We are in the business of producing electricity, not producing documents."

However, critics pointed out the OPA does not actually produce electricity, but negotiates and signs power contracts -- or documents.

Ontario's auditor general is probing the costs of both the Oakville gas plant, which was cancelled in 2010, and the Mississauga plant, which was halted in mid-construction just weeks before the Oct. 6, 2011 election.