Let the mixture sit undisturbed until the oil and water form separate layers
Pour off the top oil layer carefully
Use a separating funnel to drain the bottom water layer first
Use a pipette or syringe to remove one layer from the other
Skim the oil off the surface with a spoon or absorbent material
Use centrifugation to speed up separation
Filter through a material designed to separate immiscible liquids
Add a demulsifier if the mixture is emulsified
Freeze the water if appropriate, then remove the oil layer after thawing begins