[en] The results obtained from approximately 4000 h of operation of an electrochemical oxygen meter developed at General Electric Company for measuring oxygen activities in liquid sodium are described. In the present design, a small ceramic cup (ThO₂ with 7 to 8 wt % Y₂O₃) has been brazed to a metal tube that is inserted into the liquid sodium via a standard sodium flange. The reference electrode used in the present design consists of In/In₂O₃. Several meters were tested in a flowing sodium system, where the oxygen concentrations were controlled by a cold trap. At 500⁰C, the oxygen electromotive force (emf) output can be expressed as emf/sub (V)/ = 0.269 + (160/T) (+-0.003 V), where T is the cold-trap temperature in K. The temperature coefficient of the meters can be expressed as (dE/dT) = 0.51 +- (0.02) mV/⁰C