Abstract: A waste heat utilization system for an internal combustion engine in a motor vehicle is provided. The system includes a waste heat utilization circuit in which a working medium circulates and has in succession in the flow direction of the working medium a pumping device, at least one vaporizer, an expansion machine for depressurizing, and a condenser. The system also includes a pressure reservoir, which has a cylinder which encloses the balancing volume, and a separating piston, which separates the balancing volume from a gas volume in the cylinder, is arranged in the cylinder. The balancing volume can be actively adjusted by way of an adjusting device and the adjusting device has an adjusting piston which axially constrains the gas volume. The separating piston is arranged in the cylinder, and the adjusting device has an actuator for adjusting the stroke of the adjusting piston.