Abstract: A hydraulic motor has a sliding-vane circular rotor disposed in a substantially elliptically cylindrical rotor chamber formed in a body to which the rotor is rotatably mounted so as to define a pair of diametrically opposed arcuate work cavities. Working fluid is introduced under pressure to each of the cavities via an inlet port, and spent working liquid is withdrawn from each cavity via an exit port. Each exit port is displaced angularly from the inlet port in the direction of rotation of the rotor. The rotor carries a sufficient number of radially movable, spring biased vanes, which are slidably engageable with the walls of the chamber, that at least one vane is always disposed in cavity-dividing position in each cavity for application thereto of pressure of liquid in the cavity between the vane and the inlet port. Working liquid pressure is applied to the vane to urge the vane toward the outlet port and to turn the rotor about an axis of rotation thereof.