A pump comprising a regenerative pumping mechanism having a generally disc-shaped rotor mounted on an axial shaft for rotation relative to a stator. The rotor has first and second surfaces each having a series of shaped recesses formed in concentric circles thereon, and a stator channel formed in a surface of the stator which faces one of the rotor's first or second surfaces. The rotor divides the a gas flow path into sub-flow paths such that gas can flow towards the outlet simultaneously along both the first surface and the second surface of the rotor.