The production of hydrogen from methane via two chemical looping reforming (CLR) processes was simulated and thermodynamically analysed, one process being the conventional CLR process, the other being a CO2 sorption enhanced process. The aim of the work was to identify suitable operating conditions for obtaining an optimum hydrogen gas purity and yield, whilst operating auto-thermally, at atmospheric pressure and with no carbon formation. In both simulations, the reactors were simulated using the Gibbs minimisation technique. NiO was used as the oxygen storing species, whilst CaO was used as the CO2 adsorbent. For conventional CLR, within the range of conditions tested, the optimum reactor operating conditions are a temperature of 800 degrees C, a H2O/CH4 ratio of 3, and a NiO/CH4 ratio of 1 resulting in an approximate hydrogen production yield of 2.5 mol of H-2 per mole of CH4 and an approximate hydrogen purity of 75%. However, with the application of in situ CO2 adsorption, a hydrogen purity>90% and a yield within the region of 3 mol of H2 per mole of CH4, can be achieved with a NiO/CH4 ratio 1, a CaO/CH4 ratio >1, a H2O/CH4 ratio > 2 and a temperature between 500 degrees C and 600 degrees C. The results indicate that the implementation of in situ CO2 adsorption could potentially bring about significant improvements in both yield and purity of hydrogen. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.