Dense La0.6Sr0.4CoO3 (LSC) and La0.81Sr0.09MnO3 (LSM) were prepared by laser ablation on samaria-doped ceria (SDC) and yttria-stabilized zirconia (YSZ) substrates, respectively. The interfacial conductivity of the dense LSM electrodes was independent of the oxygen partial pressure and inversely proportional to the thickness of the LSM film. On the other hand, the interfacial conductivity of the dense LSC electrode was proportional to the square root of the oxygen partial pressure, which indicates the sensitivity of the surface reaction to the overpotential. To determine the origin of the overpotential, we constructed a surface-reaction model. Good agreement was found between our model and experimental results. (C) 2000 Elsevier Science B.V. All rights reserved.