In 2006, energy-related CO2 emissions from transport energy in Ireland were 168% above 1990 levels. Private cars were responsible for approx 45% of transport energy demand in 2006 (excluding fuel tourism). The average annual growth of new cars between 1990 and 2006 was 5.2%. This paper focuses on these new cars entering the private car fleet, in particular the purchasing trend towards larger size cars. This has considerably offset the improvements in the technical efficiency of individual car models. The analysis was carried out on the detailed data of each individual new vehicle entering the fleet in 2000-2006. The average CO2 emissions per kilometre for new petrol cars entering the Irish fleet grew from 166 to 168 g CO2/km from 2000 to 2005 and reduced to 164 in 2006. For diesel cars the average reduced from 166 in 2000 to 161 in 2006. The paper also discusses how a recent change in vehicle registration taxation and annual motor tax had a significant impact purchasing trends by supporting lower emission vehicles. Cars with emissions up to 155 g CO2/km represented 41% of new private cars sold in Ireland in 2007 compared with 84% during the period July-November 2008. (C) 2009 Elsevier Ltd. All rights reserved.