The cleanup of the Mediterranean region constitutes one of the main chapters carried by the cooperation between both north and south banks within the framework of the Union for the Mediterranean (UfM). The subject of this paper is to study the relationship between CO2 emissions and economic growth in UfM countries. This relationship is described by the so called Environmental Kuznets Curve (EKC) model. The choice of model specification and the omission of additional variables appear among the controversies revealed around the EKC modelling. At first, this paper aims to select a model among three proposed. Secondly, it examines the effect of trade and population density on CO2 emissions. Three main results are attributed by this work. First, while CO2 emissions are still in increase in the case of MEDA countries, they have known a reduction phase in the case of UE countries. Second, the shape of the EKC as well as the turning point value depends on the functional form choice. Finally, the creation of a free trade area between both Mediterranean banks does not seem to affect the environment quality.