The extrusion of EPDM compounds with a two-stage vented screw has been studied. Experimentally, the pressures and temperatures were measured at the end of each stage, for different processing conditions (screw speed, die geometry etc.). Screw pulling experiments have allowed to observe the partially filling of the different screw sections. Assuming a power-law pseudoplastic behaviour for the rubber compound, the flow in each stage of the screw has been computed. The evolutions of the pressure and the temperature all along the screw, as well as the filling length of the second stage are then obtained. The theoretical results are in good agreement with the experimental measurements.