The distribution of the mitigation burden across countries is a key issue regarding the post-2012 global climate policies. This article explores the economic implications of alternative allocation rules, an assessment made in the run-up to the COP15 in Copenhagen (December 2009). We analyse the comparability of the allocations across countries based on four single indicators: GDP per capita, GHG emissions per GDP, population growth, and the GHG emission trend in the recent past. The multi-sectoral computable general equilibrium model of the global economy, GEM-E3, is used for that purpose. Further, the article also compares a perfect carbon market without transaction costs with the case of a gradually developing carbon market, i.e. a carbon market with (gradually diminishing) transaction costs.JRC.J.1-Economics of Climate Change, Energy and Transpor