In order to quantitatively evaluate the risk associated with the Carbon Capture and Storage (CCS) technology, a deeper understanding of CO2 dispersion resulting from accidental releases is essential. CO2 is a heavier-than-air gas. Its dispersion patterns may vary according to local conditions. This study focuses on CO2 dispersion over complex terrains. Computational Fluid Dynamics (CFD) models were developed to simulate the CO2 dispersion over two hypothetical topographies: (1) a flat terrain with an axisymmetric hill and (2) a simplified model of an urban area with buildings. The source strength, wind velocity and height of the buildings were varied to investigate their effects on the dispersion profile. The study may offer a viable method for assessment of risks associated with CCS.