Powders of CaO sorbent modified with CaZrO3 have been synthesized by a wet chemical route. For carbonation and calcination conditions relevant to sorbent-enhanced steam reforming applications, a powder of composition 10 wt % CaZrO3/90 wt % CaO showed an initial rise in CO2 uptake capacity in the first 10 carbonation-decarbonation cycles, increasing from 0.31 g of CO2/g of sorbent in cycle 1 to 0.37 g of CO2/g of sorbent in cycle 10 and stabilizing at this value for the remainder of the 30 cycles tested, with carbonation at 650 degrees C in 15% CO2 and calcination at 800 degrees C in air. Under more severe conditions of calcination at 950 degrees C in 100% CO2, following carbonation at 650 degrees C in 100% COD the best overall performance was for a sorbent with 30 wt % CaZrO3/70 wt % CaO (the highest Zr ratio studied), with an initial uptake of 0.36 g of CO2/g of sorbent, decreasing to 0.31 g of CO2/g of sorbent at the 30th cycle. Electron microscopy revealed that CaZrO3 was present in the form of <= 0.5 mu m cuboid and 20-80 nm particles dispersed within a porous matrix of CaO/CaCO3; the nanoparticles are considered to be the principal reason for promoting multicycle durability.