Oil in wastewater causes environmental problems. The official control method of its content is, at present, done by extraction and subsequent measurement via IR absorption. There has been an increasing interest in continuous measurements. The method discussed in this paper is fluorescence measurement. The molecules of many oil components are exited in the UV and yield fluorescent light in the VIS range. The "sum parameter" of fluorescence is neither identical with that of IR measurement nor that of the total oil mass. Thus, these data correlate only if the composition of the oil does not change drastically. That means in general that a calibration is good only for one specific oil and for the corresponding drilling site. A factory calibration is discussed and compared with the situation on site. It will be shown which measuring ranges are realistic for this method. An optical schematic of a dual beam fluorescence photometer for continuous oil measurements is introduced. This setup allows drift flee measurement and accounts for interferences of solids in a moderate concentration. A solution to prevent finding and the required steps are introduced.