The aim of this work is to investigate the limit performance of molten carbonate fuel cells due to gas diffusion phenomena in the porous electrodes when high reactant utilisation factors are used. Modelling and experimental activities are presented. An electrode kinetic micromodel has been performed accounting for the effects of the diffusion limits and has been integrated into a macromodel in order to optimise cell performance and operation. Specific tests have been carried out to identify the dependence of anodic as well as cathodic limiting current density on operating parameters using planar square cells produced by Ansaldo Ricerche (ARI). In turn, limiting current measurements have been used in order to identify overall reactant mass transfer coefficients in the complex structure of the electrodes. A good agreement between simulated and experimental results is presented and discussed.