Potentiometric sensors using different solid electrolytes, including proton, oxide-ion, and mixed proton and oxide-ion conductors, were fabricated to investigate a relationship between the mixed potential for Cl-C4 hydrocarbons and ion conduction in the electrolyte in a mixture of hydrocarbons and oxygen at 600 degreesC. There was an increase in the mixed potential for the hydrocarbons with increasing proton conductivity or decreasing oxide-ion conductivity. The sensor using a SrCeo(0.9)5Yb(0.05)O(3)-(alpha) (SCY) electrolyte with a Pt electrode showed an enhancement of the mixed potential for the hydrocarbons by increasing the carbon number, branching the chain structure, and unsaturating the C-C linkage. The polarization curves for hydrocarbon oxidation and for oxygen reduction at the Pt/SCY interface were also measured. These results revealed that the mixed potential at the Pt/SCY interface was strongly dependent on the rate of abstraction of hydrogen atom from the hydrocarbon molecules.