The electronic conductivity of Ce(0.9)Gd(0.1)O(1.95-δ) and Ce(0.8)Pr(0.2)O(2-δ) under suppressed ionic flow was measured as a function of pO(2) in the range from 10(3) atm to 10(-17) atm for temperatures between 600 °C and 900 °C by means of Hebb-Wagner polarisation. The steady state I-V curve of Ce(0.9)Gd(0.1)O(1.95-δ) could be well described by the standard Hebb-Wagner equation [M. H. Hebb, J. Chem. Phys., 1952, 20, 185; C. Wagner, Z. Elektrochem., 1956, 60, 4], yielding expressions for the n- and p-type conductivity as a function of pO(2). On the other hand, significant deviation of the steady state I-V curve from the standard Hebb-Wagner equation was observed for the case of Ce(0.8)Pr(0.2)O(2-δ). It is shown that the I-V curve can be successfully reproduced when the presence of the redox active dopant, Pr(3+)/Pr(4+), is taken into account, whereas even better agreement can be reached when further taking into account the interference between the ionic and electronic flows [C. Chatzichristodoulou, W.-S. Park, H.-S. Kim, P. V. Hendriksen and H.-I. Yoo, Phys. Chem. Chem. Phys., 2010, 12, 33]. Expressions are deduced for the small polaron mobilities in the Ce 4f and Pr 4f bands of Ce(0.8)Pr(0.2)O(2-δ).