Dense and porous samples of a mixed conducting material of composition of Ba3Ca1.18Nb1.82O9-delta (BCN18) were fabricated. The electrical conductivity was measured over a partial pressure of oxygen, po(2), range from 0.001 to 1 atm and over a temperature range from 500 to 700degreesC. The experimental results showed that the electrical conductivity of the material is predominantly due to electron-hole conduction in the po(2) and the temperature range investigated. The measured total conductivity as a function of po(2) could be described by an equation of the form sigma(1) = sigma(i) + fp(o2)(1/4) with good accuracy. By fitting to this equation, the conductivities due to oxygen ions and due to electron-holes were separately determined. Conductivity measurements were also carried out in H2O-containing atmospheres. In H2O-containing atmospheres with proton conduction present, the sum of proton conductivity and oxygen ion conductivity can also be determined by the same procedure. The activation energies for oxygen ion conduction and electron-hole conduction were estimated to be 0.54 and 0.84 eV, respectively. (C) 2004 The Electrochemical Society.