Oil-in-water (O/W) emulsions used in machining processes were treated in a laboratory bottle centrifuge and in a pilot-scale disc-stack centrifuge. Small amounts of a coagulant salt (CaCl2, in the concentration range 0.01-0.5 M) were added to promote emulsion destabilization and to improve centrifugation. Grade efficiency curves were obtained from droplet size distribution measurements of the emulsion after centrifugation. The effect of the amount of coagulant salt on emulsion breakdown was studied by zeta potential and turbidity measurements. The effect of several parameters, such as angular velocity or centrifugation time on the critical diameter and grade efficiency was also investigated. Oil removal efficiencies of 92-96% were obtained for all centrifugation experiments.