There is a growing interest in developing high temperature CO2 capture looping systems using CaO as a regenerable sorbent. The evolution of the sorbent properties with the number of cycles plays an important role in the design of these systems. One of the key variables to be determined is the sorbent's CO2 carrying capacity at the end of the so called fast carbonation stage. This is the only useful conversion for practical purposes and it is known to decrease with the number of cycles. It is obviously important to obtain experimental CaO deactivation curves from sorbent laboratory tests in conditions as close as possible those to an industrial system. This paper reviews previously reported results and investigates the effect of carbonation conditions on the CO2 carrying capacities of CaO. An upgraded version of an existing deactivation model is used to provide a better interpretation of the sorbent deactivation trends observed. The inclusion in the deactivation model of an additional diffusion controlled carbonation stage may help to explain some important discrepancies and observations reported in the literature. This review highlights the need for an improved methodology to avoid the distortional diffusional effects in the determination of CaO deactivation curves. (c) 2010 Elsevier B.V. All rights reserved.