In an effort to develop a novel hydrogen production process in which coal is gasified with high-pressure steam in the presence of CO2 sorbents, the fundamental CO2 sorption characteristics of Ca-based sorbents during repetitive carbonation-calcination reactions at different pressures were investigated using a conventional TG/DTA analyzer and a laboratory-scale horizontal-tube reactor. The results revealed that, as a result of sintering and crystal growth, Ca-based sorbents were significantly deactivated by high-temperature calcination treatment. As a consequence, the CO2 uptake capacity of the sorbents decreased with cycle number under both atmospheric and pressurized conditions. An intermediate hydration treatment was found to enhance the reactivity and durability of the sorbents for multicycle CO2 sorption. Because of the presence of eutectics in the CaO-Ca(OH)(2)-CaCO3 ternary system, the formation of sorbent melts was observed in repetitive calcination-hydration -carbonation reactions at elevated pressures at 923 and 973 K. Even under eutectic conditions, the sorbents retained their high reactivity for CO2 sorption.