Video shows simulation of air compression with oil injection in the chamber of a 4/5 rotary screw compressor. The face area of discharge port is visible and velocity vectors shows the highly transient nature of gasoil flow entering the discharge through the rotors. Oil volume fraction is plotted from 0 to 25% range in a cross section. A small concentration is also seen on the suction side has has been practically observed during measurements. Dynamics of the Interaction of injected oil and the rotor lobes in the chamber are well illustrated by this CFD model. Details of these interactions are important for optimum oil injection design.