The main characteristics and performance of a zirconia single crystal in oxygen sensors at low temperatures are investigated by electrochemical methods in both gaseous and molten metal environments. The O-2-sensing properties of the sensors based on a zirconia single crystal in combination with molten in + Zn2O3 and Pi + Bi2O3 reference electrodes were examined. Tested materials for the measuring electrode included (U, Pr)O2+x + Pt, (U,Sc)O2+x + Pt, porous Pt and Pt-ZrO2-Y2O3 thin-film. Pt-ZrO2-Y2O3 thin-film was the most effective in promoting oxygen transfer at temperatures as low as 360-600 degrees C. Pt-ZrO2-Y2O3 thin-film was also less affected by being in adaptation exposure to high temperature. Results indicate that the sensor based on a zirconia single crystal with a Bi + Bi2O3 reference electrode can not only work at low temperatures, but also at high temperatures. The developed oxygen probe based on a zirconia single crystal appears to operate satisfactorily in both a gaseous environment and with low-melting or high-melting metals and their alloys. Some of these metals were not previously considered for in-situ monitoring. The electromotive force (EMF) response of each sensor closely followed the Nernst equation.