The development of the Carbon Capture and Storage (CCS) technique requires an understanding of the hazards posed by the operation of high-pressure CO2 pipelines. To allow the appropriate safety precautions to be taken, a comprehensive understanding of the consequences of unplanned CO2 releases is essential before the deployment of CO2 pipelines. In this paper, we present models for the predictions of discharge rate, atmospheric expansion and dispersion due to accidental CO2 releases from high-pressure pipelines. The GERG-2008 Equation of State (EOS) was used in the discharge and expansion models. This enabled more precise 'source strength' predictions. The performance of the discharge and dispersion models was validated against experimental data. Full-bore ruptures of pipelines carrying CO2 mixtures were simulated using the proposed discharge model. The propagation of the decompression wave in the pipeline and its influence on the release rate are discussed. The effects of major impurities in the CO2 mixture on the discharge rate were also investigated. Considering typical CO2 mixtures in the CCS applications, consequence distances for CO2 pipelines of various sizes at different stagnation pressures were obtained using the dispersion model. In addition, the impact of H2S in a CO2 mixture was studied and the threshold value of the fraction of H2S at the source for which the hazardous effects of H2S become significant was obtained.