In order to verify the validity of the simulation and to investigate the gaseous diffusion from the outlet of the anode, anodic gas concentration measurements of a seal-less disk-type solid oxide fuel cell (SOFC) were carried out using quadrupole mass spectrometer (QMS). Simultaneous gas sampling was conducted from the five sampling ports made at the anode separator. The uniformity of the radial gas flow in the anode was confirmed by analyzing the gas from four sampling ports located at a concentric circle. H-2, H2O and N-2 concentration profiles were measured and simulated under various fuel utilization (U-f) conditions and changing the gas flow rate. The diffusion of N-2 into the anode was found to become less with increasing Uf owing to the lesser diffusivity of N-2 in H2O than in H-2. From the simulation, the existence of the reverse current, i.e., electrolysis current, in the outlet region was predicted. It was confirmed that the existence of the electrolysis current is possible by measuring the concentration of the gas in the anode under electrolysis operations. The comparison of V-i characteristics measured and simulated revealed that the effect of the concentration polarization is not significant and suggested the validity of the assumption made for the simulation. (c) 2005 Elsevier B.V. All rights reserved.