The electrical conductivity of Ba0.85K0.15ZrO3-delta (BKZ) has been studied as a function of both oxygen and water vapor partial pressure in the temperature range of 550-700 degrees C, to determine the partial conductivities of protons, holes, and oxygen vacancies from the defect model. It is shown that p-type conduction is dominant in dry oxidative atmospheres, while in wet oxidative atmospheres, a conduction transition from proton to hole conduction is found with increasing temperature. On the contrary, in wet nitrogen atmosphere, proton conduction is dominant over the whole temperature range. The calculated activation energies for oxide-ion, electron-hole and proton conduction are 0.86, 1.36 and 0.59 eV, respectively. The standard solution enthalpy for water dissolution is -90 kJ/mol, which is lower in absolute terms than that typically reported for doped barium cerates but very close to that reported for BaZr0.85Y0.15O3-delta. (C) 2015 Elsevier Ltd. All rights reserved.