An air compressor system having a cast separator tank for use with an oil-flooded air compressor. The cast separator tank including an integrally cast airend inlet opening which is mountable in face-to-face engagement with an airend discharge opening of the compressor; an integrally cast first channel which extends between the airend inlet opening and a separation chamber; an integrally cast second channel which communicates with a lower portion of the separation chamber and which extends along an outer portion of the cast separator tank; and an integrally cast lip which extends around an inner wall of the separation chamber. The compressor system further having a motor, such that the compressor, the motor and the cast separator tank are attached to form a single unit for ease of handling. The compressor system also has a plurality of mounting feet for attachment to an appropriate subbase.