A pump comprises a regenerative pumping mechanism. A rotor of the pump has a generally disc-shaped pump rotor mounted on an axial driveshaft for rotation relative to a stator, the pump rotor having rotor formations disposed in a surface and defining at least a portion of a flow path for pumping gas from an inlet to an outlet. The rotor formations are formed between the pump rotor and the stator of the pumping mechanism. The pump rotor and the stator comprise an axial gas bearing arrangement for controlling axial clearance between the rotor and the stator during pump operation. The gas bearing is located at a radially outward position on the rotor.