The design of European mitigation policies requires a detailed examination of the factors explaining the unequal emissions in the different countries. This research analyzes the evolution of inequality in CO2 emissions per capita in the European Union (EU-27) in the period 1990-2009 and its explanatory factors. For this purpose, we decompose the Theil index of inequality into the contributions of the different Kaya factors. The decomposition is also applied to the inequality between and within groups of countries (North Europe, South Europe, and East Europe). The analysis shows an important reduction in inequality, to a large extent due to the smaller differences between groups and because of the lower contribution of the energy intensity factor. The importance of the GDP per capita factor increases and becomes the main explanatory factor. However, within the different groups of countries the carbonization index appears to be the most relevant factor in explaining inequalities. The policy implications of the results are discussed. (C) 2013 Elsevier Ltd. All rights reserved.