The use of membranes to treat oil-water emulsions is increasing, especially in applications where the value of the recovered materials is high, e.g., recycling aqueous cleaners and machining coolants. For separation of oil emulsions as an end-of-pipe treatment, membranes are more likely where process volumes are less than 50 000 gal (190 m(3)) per day. Membranes could also be useful in a hybrid system when it is combined with conventional chemical treatment systems to concentrate sludges. This review describes several case studies of these applications, and discusses the possible pitfalls and potential of in applying membranes to the treatment of oily wastes.