The Ontario Power Authority revealed Thursday that it failed to release all of the documents related to two cancelled gas plants that costs Ontario taxpayers hundreds of millions of dollars after the issue prompted a heated question period in the Ontario legislature earlier in the day.

The agency said Thursday that 67 documents were inadvertently missed when it turned over the latest batch of gas plant documents to the government in October.

“Large-scale document disclosures are something that many, many agencies struggle with and have difficulty getting right,” OPA Chair Jim Hinds told reporters. “We are no exception.”

Earlier Thursday, Energy Minister Bob Chiarelli revealed that additional records relating to the two mega projects in Oakville and Mississauga were uncovered this week, even after the Liberal party said it turned over all related gas plant documents.

The OPA said it failed to use certain key words when in their search for gas plant documents, prompting the oversight.

Hinds said the newly-released documents are largely made up of meeting notices and invoices -- though the invoice amounts have already been made public.

“We are in the business of producing electricity, not documents,” Hinds said, adding that the gas plant documentation was the first large-scale document search the agency had ever undertaken.

Both Hinds and OPA CEO Colin Andersen were asked repeatedly if there was any political interference in releasing the documents -- a question Hinds said couldn’t be answered with a simply ‘yes or no’.

“We’re here today to talk about this additional 67 documents and I think that’s about as far as we can go out of respect for the legislature,” he said.

Andersen also said a member of the energy minister’s office did visit the OPA during the search, but only to look at the documents.

“We are also dealing with information that is commercially sensitive, that is subject to privilege,” Andersen said. “It’s very important that we protect information and provide it appropriately and make sure nothing inadvertently gets out that shouldn’t.”

The OPA execs could not say how much it cost to axe the gas plants and instead pointed to an auditor general’s report on the issue that’s expected to be released this spring.

The Liberals have pegged that cost at $230 million, though the opposition claims the actual number is much higher.

Opposition slams Liberals over gas plant docs

NDP Leader Andrea Horwath said she was “completely shocked” by news of the additional documents.

The Liberals initially released a batch of documents in September and told the legislature there were no more documents related to the matter. A month later, another 20,000 documents were found.

“The government insisted that all documents had been disclosed, then more were discovered, and now (even) more have been discovered,” Horwath said during question period on Thursday. “Is there any reason at this point in time that any person in this province should believe this government has any credibility whatsoever on the issue of the moved gas plants?”

Horwath yet again pressured Premier Kathleen Wynne to agree to a third-party public inquiry on the matter, through the Premier said the inquiry would be too costly.

Wynne insisted that since launching her Liberal leadership campaign, she made it a priority to ensure that every single piece of information on the cancelled gas plants was disclosed.

“We’re not talking about boxes of paper, we’re talking about electronic information that has to be searched out,” Wynne told the legislature.

“I would have obviously preferred to have been able to say that every single document, every single piece of electronic material, that was created has been found. It is as ongoing process.”

Wynne also pointed out that both the NDP and the Tories have publically said the locations of the cancelled gas plant were inappropriate.

Both the NDP and the Tories have said the costly decision was made to save Liberal seats in the riding ahead of the October 2011 provincial election.