A scroll compressor includes 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 the trapped volume between the 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 the trapped volume along a second portion 64 of the flow path, and the first portion is closer to the inlet than the second portion along the flow path.