This paper discusses briefly a number of separation techniques for the treatment of water produced during oil production and gives some advantages and drawbacks. Plate separation and centrifugation are subject to investigation in our laboratory; these techniques are treated in more detail. The characteristic parameters "critical oil droplet diameter" and "separator capacity" are defined, and for both plate separation and centrifugation an example of a calculation with these parameters is given. Furthermore some results of laboratory experiments are presented. Finally, ideas for improving both the plate separation technique and the centrifugation technique are discussed. It is expected that critical oil droplet diameters of about 10 μm (plate separation) and less than 1 μm (centrifugation) are achievable.