The Kyoto Protocol covers emissions of a range of greenhouse gases. Yet, most attempts to quantify the economic impact of implementing the Protocol’s emission targets for the period 2008-12 have focused exclusively on CO2 emissions. This paper extends previous OECD analysis confined to CO2 alone so as to cover also emissions of methane and nitrous oxide. The paper concludes that the economic costs of implementing the targets in the Kyoto Protocol are lower than suggested by an analysis confined to CO2 alone. However, over the longer term, when larger cuts in greenhouse gas emissions are required in order to have any material effect on climate, most abatement will likely have to come from CO2 and the inclusion of other gases in the analysis may not substantially alter estimates of economic costs ...