Ce0.8Sm0.2O1.9-delta powders were prepared by a freeze drying method and used to obtain ceramic disks. These samples were used to study the electronic transport properties of this material. A Hebb-Wagner method was used to obtain the electronic conductivity under ion blocking conditions. Typical values of electronic conductivity measured for this material at 800 degreesC were about 0.37 S m(-1) at Po-2 = 10(-16) atm and 0.58 S m(-1) at Po-2 = 10(-18) atm. These values are significantly lower than results reported for ceria-based materials with different trivalent additives. A coulometric titration method was used to estimate the charge carrier concentrations, and the mobility of carriers was obtained on combining the results of conductivity and concentration. Typical values of mobility show weak temperature dependence and decrease with increasing oxygen deficiency, suggesting a limiting value of about 0.5 x 10(-7) m(2). V-1 s(-1) for relatively high delta. (C) 2003 Elsevier Ltd. All rights reserved.