Various institutions in the government, business, and investment communities are now demanding and relying on credible, comparable, consistent sustainability (economic, social, and environmental) information for decision making, especially related to greenhouse gas (GHG) emissions. Based on GHG emissions reports, governments are developing policy to ensure adherence to reduction commitments under worldwide agreements which in turn affect corporations’ planning and investment requirements. As well, investors want to know how these commitments will affect their returns. Organizations have answered the demand by providing GHG information to their shareholders through a number of reporting channels. As each channel provides its own guidelines for reporting, the question arises as to how consistent are the numbers reported under the various channels? We investigate the reliability of reporting of GHG emissions by corporations available through three different channels: mandatory reporting under government regulations; voluntary reporting under the CDP; and voluntary reporting through the companies’ stand-alone sustainability report.