Carbon capture and storage (CCS) is considered a leading technology for reducing CO2 emissions from fossil-fuelled electricity generation plants and could permit the continued use of coal and gas whilst meeting greenhouse gas targets. However considerable energy is required for the capture, compression, transport and storage steps involved. In this paper, energy penalty information in the literature is reviewed, and thermodynamically ideal and "real world" energy penalty values are calculated. For a sub-critical pulverized coal (PC) plant, the energy penalty values for 100% capture are 48.6% and 43.5% for liquefied CO2, and for CO2 compressed to 11Â MPa, respectively. When assumptions for supercritical plants were incorporated, results were in broad agreement with published values arising from process modelling. However, we show that energy use in existing capture operations is considerably greater than indicated by most projections. Full CCS demonstration plants are now required to verify modelled energy penalty values. However, it appears unlikely that CCS will deliver significant CO2 reductions in a timely fashion. In addition, many uncertainties remain over the permanence of CO2 storage, either in geological formations, or beneath the ocean. We conclude that further investment in CCS should be seriously questioned by policy makers.