In a hydraulic machine, especially a high-pressure hydraulic pump with pistons (5) driven by a wobble rotor (8), the angle (14) between the axis of any one roller (13) in the rotor bearing (11, 12, 13) and the axis (3) of the machine's drive shaft (4) is of the order of 30 to 60 angular degrees, preferably of the order of 40 to 50 angular degrees (approximately 45 degrees in the example shown). The use of an angle (14) within the ranges mentioned causes a reduction of the bearing surface pressure on the roller races (11, 12), thus also making it possible to form one (12) of said races integral with the wobble rotor (8), and also to use cylindrical rollers (13) instead of the more costly conical ones normally used in such machines.