A program was carried out to develop small less fragile ceramic electrodes for use in measuring oxygen in sodium. To use the electrodes as inserts in existing sampler hardware, composite metal-ceramic tubes were required. Four configurations of composite metal-ceramic probes employing yttria-doped thoria as the solid electrolyte were fabricated and tested. These incorporated both mechanical and brazed seals between the metal and ceramic. The most useful for fast flux test facility applications utilized a brazed seal between the ceramic and an alloy of matching coefficient of thermal expansion. A number of alternate reference systems were also investigated. Reference electrodes tested included Na-Na2O, In-In2O3, Ni-NiO, and Ag-air.