TORONTO – A look at some of the biggest merger and acquisition deals involving Canadian companies in 2012:

China National Offshore Oil Co. (CNOOC) signed a deal to buy oil and gas producer Nexen Inc. (TSX:NXY) for $15.1 billion in cash in one of the biggest deals of the year. The takeover bid became the focus of national attention as Ottawa approved it under the Investment Canada Act, but shut the door on future oilsands deals involving state-owned businesses except under exceptional circumstances.