The initial and long-term drift of tcPO2 microcathode electrodes has been shown to be substantially less when chloride is removed from the electrolyte, despite the probability that reference electrode EMF is less well defined. In addition to virtually eliminating drift, these electrolytes eliminate silver deposition on the cathode. The most successful electrolyte tested thus far has been 0.2 M K2B4O7 in 95% ethylene glycol, 5% water, both with and without cellophane spacers. The buffering produced by borate appears to prevent the downward drift in CO2 free air probably caused by Ag2 CO3 formation on the anode, after exposure to skin.