Undoped ceria with its facile redox at high-temperatures has potential as an effective material for electrolysis. This study explores the electrochemical performance of thin-film ceria electrodes for H2O electrolysis at 700 °C. The electrochemical characterization is complemented by in situ XPS measurements, which show that the highly reduced ceria surface increases in degree of reduction with electrolysis voltage. Results also show that H2O electrolysis is enhanced with increased H2 partial pressure. Analysis of electrochemical impedance spectra and voltammetric measurements show that the electrolysis reactions depend strongly on H2 pressure. These trends, which are not readily explained by simple surface kinetic models, do indicate that increased ceria surface reduction by the presence of H2 product enhances activity for H2O electrolysis. The results were used to create a microkinetic model to assess surface and subsurface processes in ceria for H2O electrolysis.