Oil-water emulsions are found in effluents from many sources, such as petroleum refineries, rolling mills, chemical processing and manufacturing plants. The requirements for the discharge of oily wastewaters have become more stringent in recent years in the course of the implementation of the environmental protection policy of the European Union. The treatment of waste emulsified oils is of environmental and commercial interest due to their detrimental effects on aquatic life and their interference with conventional wastewater treatment processes. Currently available treatment methods can be classified into three broad groups: chemical, mechanical and electrical. The chemical techniques discussed in this paper are coagulation or flocculation of the emulsified oil droplets and destruction or removal of the surfactants from the oil-water interface. The mechanical techniques discussed are filter coalescence, filtration-adsorption and membrane processes (UF, MF, NF and RO). Dissolved air flotation (DAF) is also included within these techniques, although it involves the use of chemicals. The electrical methods discussed are electroflotation, electrocoagulation and electrocoalescence. Finally, integrated separation processes are also described.