A hydraulic pump comprising a rotor provided for rotation about a longitudinal axis within a housing, the pump comprising: a plurality of chambers for pumping a fluid, the chambers being provided by longitudinally extending recesses in a circumferential outer surface of the rotor, the recesses being moved across a circumferential inner surface of the housing during rotation of the rotor, and in so doing, being moved over an inlet port in the housing to draw fluid into the chamber and then over an outlet port in the housing to discharge the fluid, wherein the hydraulic pump further comprises a roller that is mounted in a longitudinally extending pocket of the housing, the roller being positioned after the outlet port in a direction of the rotor's rotation, the roller further being arranged to follow the outer surface of the rotor and seal against each recess as it is drawn past the roller, thereby directing fluid from the chamber into the outlet port; the pump characterised by comprising a plurality of groups of an inlet port followed by an outlet port and an associated roller; the groups being arranged sequentially around the circumferential inner surface of the housing in the direction of rotation of the rotor, so that each recess of the rotor is drawn past each group in turn during a full rotation of the rotor; wherein the inlet ports are in fluid communication with each other via an inlet gallery comprising a plurality of radially extending inlet channels which are linked by an inlet ring (29a-c) extending circumferentially around the housing; and/or the outlet ports are in fluid communication with each other via an outlet gallery comprising a plurality of radially extending outlet channels which are linked by an outlet ring (31a-c) extending circumferentially around the housing. a plurality of chambers for pumping a fluid, the chambers being provided by longitudinally extending recesses in a circumferential outer surface of the rotor, the recesses being moved across a circumferential inner surface of the housing during rotation of the rotor, and in so doing, being moved over an inlet port in the housing to draw fluid into the chamber and then over an outlet port in the housing to discharge the fluid, wherein the hydraulic pump further comprises a roller that is mounted in a longitudinally extending pocket of the housing, the roller being positioned after the outlet port in a direction of the rotor's rotation, the roller further being arranged to follow the outer surface of the rotor and seal against each recess as it is drawn past the roller, thereby directing fluid from the chamber into the outlet port; the pump characterised by comprising a plurality of groups of an inlet port followed by an outlet port and an associated roller; the groups being arranged sequentially around the circumferential inner surface of the housing in the direction of rotation of the rotor, so that each recess of the rotor is drawn past each group in turn during a full rotation of the rotor; wherein the inlet ports are in fluid communication with each other via an inlet gallery comprising a plurality of radially extending inlet channels which are linked by an inlet ring (29a-c) extending circumferentially around the housing; and/or the outlet ports are in fluid communication with each other via an outlet gallery comprising a plurality of radially extending outlet channels which are linked by an outlet ring (31a-c) extending circumferentially around the housing.