Mulroney's comments were a reference to the proposed takeover of Nexen by China's National Offshore Oil Corp.
The $15-billion takeover bid of the Calgary-based company is under review.
Mulroney was clear in his opinion that foreign cash is necessary to grow the energy sector.
"Canada, and western Canada, cannot function without foreign investment. The oil and gas industry requires massive foreign investment to develop the oilsands and other major projects."
He said he expects the Keystone XL pipeline to be approved by the United States, regardless of who becomes president.
Mulroney spoke to a crowd of 600 at the Telus Convention Centre on Tuesday night.