TORONTO -- The former secretary of the Ontario cabinet says the Liberal government knew so-called "sunk costs" were just one area that would add to the bills for cancelled gas plants in Oakville and Mississauga.

An auditor general's report released Monday on the cancelled gas plant in Mississauga shows the Liberals low-balled the $275 million cost of scrapping that project by $85 million.

Shelly Jamieson, once the head of the public service, testified today that "there were buckets of costs" for cancelling gas plants, and that sunk costs -- costs already incurred that cannot be recovered -- was just one category.

Jamieson said everyone knew trying to reach deals with the developers of the two cancelled projects had the potential to cost a lot of money.

The Liberals have always maintained it cost $40 million to cancel the planned gas plant in Oakville in 2010, but admitted the province also paid $210 million for turbines for the plant.

Ontario will also need to spend another $200 million on transmission lines, but the Liberals say they would have been needed anyway.