The property of fluids to form distinct and separate phases under all relative proportions. For example, oil and water are immiscible in which oil floats on water due to its lesser density. Immiscible fluids are used in liquid–liquid extraction processes in which a solute is transferred from one phase to the other by contacting the two fluids. This often requires a large interfacial surface which can be achieved by stirrers, pulsed columns, and in mixer-settlers.