This paper presents a risk assessment methodology for high pressure CO2 pipelines developed at the Health and Safety Laboratory (HSL) as part of the EU FP7 CO2Pipehaz project. Until recently, risk assessment of dense phase and supercritical CO2 pipelines has been problematic because of the lack of suitable source term and integral consequence models that handle the complex behaviour of CO2 appropriately. The risk assessment presented uses Phast, a commercially available source term and dispersion model that has been recently updated to handle the effects of solid CO2. A test case pipeline was input to Phast and dispersion footprints to different levels of harm (dangerous toxic load and probit values) were obtained for a set of pipeline specific scenarios. HSL's risk assessment tool Quick-Risk was then used to calculate the individual and societal risk surrounding the pipeline. Knowledge gaps that were encountered such as: harm criteria, failure rates and release scenarios were identified and are discussed. Crown Copyright (C) 2013 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers. All rights reserved.