The modifications induced by oxygen on the impedance spectra of Pt/YSZ (platinum/yttria-stabilized zirconia) interfaces at 900 degrees C have been studied. Oxygen atmosphere and oxygen transfer utilizing both positive and negative direct currents influenced the concentration of oxygen-containing species (OCS) at the interface and that is shown to affect the shape of the impedance response. Two main types of OCS have been identified. The effect of chemical stripping of the OCS by utilizing a reducing CO-CO2 atmosphere was also investigated. A mechanism for oxygen transfer across the Pt/YSZ interface is suggested. It involves two parallel paths : direct, fast interfacial transfer of the O2- and a slow path, wherein the OCS participate.