Surface transportation of carbon dioxide will be a critical issue in the developing field of carbon capture and storage (CCS). A leak from a high-pressure transportation facility can result in damage to the environment and hazard to people, depending on the total amount of carbon dioxide released to the atmosphere and the concentrations achieved in the proximity of the leakage. Generic Risk Assessments for CO2 transportation to date have relied on various assumptions about the behaviour of carbon dioxide after a severe pressure drop. In this study, simulations by two classes of atmospheric dispersion model (Gaussian and computational fluid dynamics, CFD) have been compared, taking representative input parameters concerning high-pressure CO2 releases from the literature. The CFD model was used to simulate a high-speed release with specified velocities with the aim of evaluating the effect of initial gas dispersion on the downwind length reached by toxic concentrations of the pollutant. Results of this investigation depict a lowering of the Risk involved in the transportation of CO2 by up to one order of magnitude, when modelling the same releases with a CFD tool, compared to the more widespread Gaussian models. The EU used results from Gaussian modelling for drawing up an Impact Assessment on the CO2 transportation within CCS. In this paper, suggestions for future preparation of CCS Risk Assessments are presented. (C) 2011 Published by Elsevier B.V.