A theory of thermopower for proton conducting oxides (PCO) with protons, oxide ions and different electron charge carriers has been developed. The thermopower a of SrCe0.95Y0.05O3-delta, BaCe0.9Nd0.1O3-delta and of a zirconium-yttrium electrolyte as a reference material was measured in both oxidizing and reducing atmospheres. The analysis of the data obtained for the region of pure protonic conduction of SrCe0.95Y0.05O3-delta using our theoretical results and including vibrational and configurational contributions to a allowed determining both the partial entropy of protons and their heat of transport. The concentrations of protons and their temperature dependences determined from the entropy term agreed well with the experimental data available from hydrogen uptake studies. (C) 2003 Elsevier B.V. All rights reserved.