Abstract: A mechanical vacuum pump having mounted in each of at least three pumping chambers a pair of intermeshing rotors. A first rotor of each pair being mounted for rotation on a first shaft passing through the chambers and a second rotor of each pair being mounted for rotation on a second shaft passing through the chambers. The first and second shafts are driven in contra-rotating directions to effect a sequential pumping action by the pairs of rotors in each chamber in respect of gas being pumped between a pump inlet and a pump outlet. The pump possesses at least one chamber with claw-type profile rotors and one ore more chambers with roots-type profile rotors. The chamber nearest the pump outlet has a rotor with a roots-type profile.