In the present work, the behavior of a MOLB-type (mono-block layer built) SOFC (solid oxide fuel cells), with different electrolyte thicknesses and operating conditions at the inlet, such as mass fraction, temperature and velocity, is numerically investigated. An entropy generation analysis is carried out in the fuel cell and it is evaluated how the operating conditions and electrolyte thicknesses affect the prediction of the thermodynamic irreversibility. For this investigation a three-dimensional CFD model was developed using the finite volume method derived from a control-volume formulation that takes into account the heat transfer, the transport of species and the electrochemical reactions. Different simulations are performed and the contribution of the local entropy generation rate is computed. The results show different trends for the current density, temperature, species, activation loss, ohmic loss and concentration loss throughout the fuel cell, and indicate that the prediction of thermodynamic irreversibilities is strongly affected by the choice of the operating conditions (e.g. inlet temperature) and the electrolyte thickness. Both local and global entropy generation rates show strong variations. The results of this work are useful in helping the designer to select the different operating conditions of a MOLB-type SOFC with lower irreversibilities. (c) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.