Transport of reactants and products to/from reactions sites affects the electrochemical energy conversion performance of fuel cells substantially. At high reactant utilization rates, mass transport can be the performance limiting factor, resulting in significant variations of current and temperature, etc. in the active field. To overcome mass transport limitations, reactants can be supplied at high rates and proper flow fields can be designed, for both of which numerical simulations are quite valuable. In these regards, although the highest care is put on the transport of species within active area of cells/stacks, herein we show the onset of mass transport limitation in the inlet periphery, i.e., extension of the concentration gradient of reactants from reactions sites inward the inlet periphery at high reactant utilization rates. We clarify this phenomenon leaning upon the computational error appearing in the concentration profile of a microtubular Solid Oxide Fuel Cell (SOFC) while simulating its electrochemical performance. For eliminating this error in numerical studies of fuel cells, we propose and demonstrate a practical method. We also determine the critical ratio of consumed/supplied mass fluxes for evaluating relevant (reactant species) SOFC systems in terms of the mass transport limitation in their inlet peripheries. (C) 2018 The Electrochemical Society.