A technological stock model of private car energy demand is built, using as explanatory variables, fleet structure, the profile of activity, and fleet efficiency. Disaggregating the three variables by vehicle technology and age produces a detailed profile of private car activity and energy consumption, giving accurate energy calculations and allowing detection of the technological drivers of energy consumption. Methods for calculating fleet on-road energy efficiency in terms of an "on-road factor" are developed. The methodology is applied in an Irish case study and results show a 37% increase in private car energy demand between 2000 and 2008, and that driving this increase was a growth in diesel and larger engine activity and the ageing of the fleet. (C) 2010 Elsevier Ltd. All rights reserved.