It is possible to estimate CO2 emissions from road freight transport in different ways, depending on the definition of trucking activity, the degree of reliance on survey, vehicle test-cycle and traffic count data and the geographical scope of the calculation. The emergence of differing road freight-related CO2 estimates from official sources and revisions to statistical series can frustrate the policy-making process and erode the confidence of industry stakeholders in the validity of the figures. Using UK data, this paper examines the various methods of carbon auditing road freight transport at the national level and compares the results both for a single year (2006) and over a time period. It highlights a series of statistical anomalies and approximations and tries to explain discrepancies that have arisen in the UK data sets. A concluding section considers the general lessons that can be learned from the recent UK experience in this field. (C) 2009 Elsevier Ltd. All rights reserved.