Possibility, of utilization of CO-containing fuel in a fuel cell based on a solid oxide protonic conductor (SOFC(H+)) is demonstrated. Thermodynamic analysis of a methane fed SOFC(H-) system is performed. It is stated that the fuel utilization depends on H2O/CH4 mole ratio in the feeding fuel mixture and has a maximum at the ratio of about 2.6. It is stated that average EMF of the SOFC(H+) is higher than that of an SOFC based on oxygen ion conductor under the same conditions and, hence, the maximum efficiency of the SOFC(H-) system is about 15% higher than of the SOFC system based on oxygen ion conductor.