The annual reporting procedures of the United Nations Framework Convention on Climate Change (UNFCCC) have now produced greenhouse gas (GHG) emission inventories from 40 so-called Annex I countries for 18 years. This article analyses a subset of these data: emissions from road transport. The article compares the reported data with the technical guidance on GHG emission inventories provided by the Intergovernmental Panel on Climate Change (IPCC). The analysis suggests that some countries use the IPCC's default emission factors, whereas other countries use country-specific values. In the case of diesel-fuelled road transport, the estimated emissions appear to be generally comparable between all countries for all years. For CO2 emissions from gasoline-fuelled road transport, the picture is less clear. The results suggest that the default emission factor for CO2 from motor gasoline as provided by the IPCC is about 3-5% too low. Countries that seem to apply this default value might therefore underestimate their emissions by the same percentage. The effect of this possible underestimate on trends is, however, very small. Despite the possible problem with the default emission factor, the quantification of the trend in emissions is only slightly influenced by this. © 2011 Earthscan.