An oil pump (10) has an inner (15) and an outer (14) rotor mounted in a cylindrical section (13) in the housing (11) and able to rotate. The rotors are in contact with each other forming chambers (17). Suction (18) and discharge (19) ducts connect to at least one of the pump chambers. A first groove (20) is located in the inner face of the cylindrical section and is connected to the discharge. A second groove (21), also in the inner face of the cylindrical section, is connected to the discharge via the first groove, whereby it lies opposite the pump chamber relative to the outer rotor. The pump chamber is evaporated fluidically from both suction and discharge ducts. Seals are located on one upper and one lower end of the second groove.
