The environmental sustainability of the air transport industry, as a key player in global social and economic development, has become a major issue in the agenda of the industry´s stakeholders during the past decade. On both international and local levels, policy makers, scientists and environmentalists, manufacturers and airlines have begun to collaborate on fuel efficiency improvements and greenhouse gas emissions reductions in the sector.This dissertation evaluates the structure and distribution of air traffic in European Union member states. The data presented here has been extracted from the statistical office of the European Union (Eurostat) and databases compiled by the The European Organization for the Safety of Air Navigation (EUROCONTROL). The focus of this study is on commercial air traffic and CO2 emissions in the European Union in 2010 and its evolution through 2013.The extracted data for all EU countries consist of variables such as: number of flights, number of passengers, freight tonnes, revenue passenger kilometers (RPKs) and revenue tonne kilometers (RTKs), fuel consumption and CO2 emissions. The majority of EU air transport traffic is concentrated in six countries: France, Germany, Italy, The Netherlands, Spain and The United Kingdom, which in 2010 represented approximately two thirds of the total EU flights. The data is then segmented per distance bands, at intervals of 500 km to see the concentration of traffic in different distance bands and compare their share with other modes of transport. The fuel efficiency trend in the six largest EU aviation markets from 2010 to 2013 is analyzed and the potential reasons for the changes are investigated. The evolution in the airline fleet composition during the last decade is presented as one of the reasons for the improvement in fuel efficiency, measured by fuel efficiency parameter measuring fuel consumption per RTK (passengers + freight). Additionally, the differences in terms of fuel efficiency among the various airline business models (network carriers, low cost carriers, etc.) and aircraft types are studied. Moreover, future CO2 emissions are projected, taking into consideration three different traffic growth and efficiency improvement scenarios.The results of this analysis indicate a slight reduction in the traffic, both for passengers and freight about (-0.8%) but more importantly, a reduction in CO2 emissions (-4.3%), which is the result of an improvement in fuel efficiency parameters (-3.5%) during these three years. There has been a relevant change in the fleet composition in the last ten years, with the replacement of older models for more efficient ones, and a shift to larger aircraft, particularly in the regional segment. Traffic has decreased in shorter distances (internal EU traffic), but increased in more efficient long-range flights (extra-EU traffic), resulting also in an improvement in the efficiency parameters as average aircraft size and stage length increases. This investigation concludes that technological efficiency in...