The purpose of the project is a preliminary descriptive analysis of the microstructure of EU CO2 emissions allowances (EUAs) markets and an assessment of market shares of German corporations in the European Union Greenhouse Gas Emission Trading Scheme (EU ETS). At first, trading rules of EUAs markets are examined and the most important market participants are identified. Subsequently a descriptive and qualitative analysis of the market microstructure of EUAs markets is conducted. Finally, market shares of single corporate entities during the second phase of EU ETS are determined (exemplarily for Germany) in order to estimate the potential degree of market power when EUAs are auctioned to domestic plant operators exclusively.