a technique for continuous gravity separation of a produced oil and water emulsion has particular utility in separating water for reinjection during a waterflood secondary recovery operation without loss of saleable oil . the method employs a flow direction means to introduce the produced oil - water emulsion into a large volume settling tank substantially tangential to the tank wall and then withdraws the separated oil and water . the apparatus of the instant invention comprises : a tank , an oil - water inlet means , a flow direction means connected to the oil - water inlet means to direct the oil - water emulsion into the settling tank tangential to the tank wall , a bottom - center located water outlet pipe , and an oil outlet pipe .