Abstract: The hydraulic machine according to the invention comprises a reservoir intended to be filled with a fluid, a rotor freely rotatably supported about a horizontal axis within the reservoir, the rotor being so shaped that the center of buoyancy and resultant force or thrust to which the rotor is subject when immersed in the fluid is not located on the axis of rotation of the rotor, and means for causing a variation in the distance between the axis of rotation of the rotor and the free surface of the fluid within the reservoir, and/or for causing a variation in the volume of the fluid within the reservoir.