ABSTRACT. The main goal of the paper is to provide the first ex-post analysis of the EU ETS in year 2013 in the Czech Republic, based on the analysis of the key EU ETS sector -combustion processes. Regarding the methodology, the empirical research was used as a one part, as a second part the Mamdani fuzzy rule-based system. Since the EUA market price was low in year 2013, the Czech companies within the combustion processes group had weak motivation to trade with the EUAs. However, the revenues obtained from the EUA auctions in year 2013 were higher than revenues obtained from the environmental taxes. Moreover, auctioned EUAs had the similar characteristics as the environmental taxes. We can say that the EUA behaved as an additional carbon tax -in case that the company exceeded the level of emission limit represented by free emission allowances.