If oxygen for propulsion and life-support needs were to be extracted from Martian resources, significant savings in launch mass and costs could be attained for both manned and unmanned missions. One method for doing this involves oxygen production from the carbon dioxide-rich Martian atmosphere using solid oxide electrolysis. This paper presents a brief theory of this process, followed by experimental results of the research performed on planar solid oxide electrochemical cells. An analysis and discussion of the experimental results is presented in an attempt to characterize the performance of solid oxide electrolyzers for oxygen separation from carbon dioxide.