A detailed mechanistic model for solid oxide electrolyte direct carbon fuel cell (SO-DCFC) is developed while considering the thermo-chemical and electrochemical elementary reactions in both the carbon bed and the SOFC, as well as the mesa-scale transport processes within the carbon bed and the SOFC electrode porous structures. The model is validated using data from a fixed bed carbon gasification experiment and the SO-DCFC performance testing experiments carried out using different carrier gases and at various temperatures. The analyzes of the experimental and modeling results indicate the strong influence of the carrier gas on the cell performance. The coupling between carbon gasification and electrochemical oxidation on the SO-DCFC performance that results in an unusual transition zone in the cell polarization curve was predicted by the model, and analyzed in detail at the elementary reaction level. We conclude that the carbon bed physical properties such as the bed height, char conversion ratio and fuel utilization, as well as the temperature significantly limit the performance of the SO-DCFC. (C) 2013 Elsevier B.V. All rights reserved.