[en] The properties of a dedicated infrared analyzer for on-line measurement of the oil content of water, the Oili analyzer, are evaluated theoretically and with laboratory measurements. The analyzer was originally developed for controlling the discharge of ballast and bilge water from oil tankers and more than 200 such instruments have now been supplied for that purpose, representing about 10 % of the total market. Some technical improvements are suggested, and the improved instrument is shown to be capable of measuring oil in water to an accuracy of +- 20 % down to a detection limit of +5-10 ppm in the presence of high concentrations of interfering components and under varying environmental conditions. This opens up new potential applications for the instrument, e.g. the monitoring of water discharges from oil and gas production platforms. The infrared analyzer responds only to the dispersed oil fraction, and if the dissolved fraction is of interest as well, the instrument must be equipped with a UV option, as suggested here