Determination of the ionic and electronic contributions to the total conductivity in mixed ionic-electronic conductors (MIEC) is central to understanding their properties, particularly in nanostructured ionic solids. The Hebb-Wagner blocking technique, commonly used to deconvolute ionic and electronic contributions in bulk MIECs, is susceptible to misinterpretation when applied to thin films. In this work, microfabricated electronic blocking electrodes consisting of porous Pt on dense thin yttria-stabilized zirconia (YSZ) films were applied to nanocrystalline CeO2 thin films. The validity of the blocking structure was expressly considered with respect to alternate current and gas phase reaction pathways, with criteria developed to aid in identifying spurious effects. The ionic partial conductivity in nanocrystalline CeO2 thin films was confirmed to be pO(2)-independent while the electronic partial conductivity was found to be pO(2) dependent with a power dependence of -0.31 +/- 0.02. These results are compared with theoretical predictions of extrinsically-compensated ceria and previous results on bulk nanocrystalline ceria. (C) 2009 Elsevier B.V. All rights reserved.