This paper analyzes the change of aggregate CO, emissions in the OECD from 1960 to 1995 based on a complete decomposition approach. The study indicates that developed countries have achieved a considerable decrease in their CO, emissions mainly due to improved energy efficiency and fuel switching. However, some member countries of the OECD have found it difficult to achieve the environmental targets set at Rio de Janeiro in 1992, and should reconsider their energy policies in light of information given at the UN Climate Change Conference in Kyoto.