Abstract: A scroll compressor comprises two scrolls (40, 46) having respective scroll plates (42, 48) and respective scroll walls (44, 50). The scroll walls intermesh so that on relative orbital movement of the scrolls a volume (52, 54) of gas is trapped between the scrolls and pumped from an inlet (31) to an outlet (33). The axial extent (A) of said trapped volume between said scroll plates is less along a first portion (62) of a flow path (56) between the inlet and the outlet than the axial extent (B) of said trapped volume along a second portion (64) of the flow path, and wherein the first portion is closer to the inlet than the second portion along the flow path.