This method is for estimating the dissolved oxygen in liquid hydrocarbons by electrochemical detection. The preferred application is online analysis, although the analysis may also be performed in the laboratory. The lower detection limit is 0.1 mass-ppm while the upper limit is dependent on the solubility of oxygen in the specific sample. Carbon dioxide, ammonia, hydrogen sulfide, and mercaptans at concentrations above 200, 300, 15 and 15-ppm (see Note 1) respectively, will interfere with the oxygen determination. Materials that contaminate the membrane or volatile components that are either oxidized, reduced, or react with the sensor electrodes will also interfere. The sampling system associated with a process unit is to be specified depending on the specific process unit.