Abstract: A method and apparatus are provided for adding controlled and accurate quantities of differing oils, to a polymer processing mixer without substantially contaminating one oil with another. Oils are contained in a plurality of oil supply tanks wherein each tank is fluidly connected to the mixer by an oil supply conduit. The speed of the oil pumped through the conduit is controlled by a variable speed pump motor drive unit. The quantity of oil passing through the conduit is preferably measured by a mass flowmeter and the measurement transmitted to a controller. A multi-directional valve controls the delivery of each oil into the mixer. The controller controls the delivery of oil into the mixer in response to the transmitted measurement, by varying the speed of the pump and opening and closing the valve.