Abstract Τhe European passenger car certification test constitutes the basis for implementation and progress monitoring of the current CO 2 abatement policy. The certification test is performed over a single driving cycle, (New European Driving Cycle-NEDC). The dynamics of NEDC and the fact that it does not account for other factors results in CO 2 emissions which are non-representative of real-world performance. Using available data from the CO 2 monitoring database and literature and employing simple vehicle dynamics model and stochastic techniques, this paper attempts to calculate the average gasoline and diesel passenger car characteristics, investigate how the evolution of certain vehicle characteristics affects real world vehicle performance and to combine the above in order to evaluate the progress in terms of real world emissions and possible correction of existing emission factors. The analysis reveals that reductions over NEDC are generally reflected over real world. There were indications particularly for diesel vehicles that the NEDC—real world CO 2 emissions gap gradually widens and that existing emission factors should be amended accordingly. Currently this difference between certification and real world emission is estimated between 20 and 25%. The benefit of diesel vehicles compared to their gasoline equivalents in terms of CO 2 emissions appears to reduce.