A delivery system for downhole use comprising an elongate delivery member, such as a length of wireline cable or coiled tubing, an injector to control the insertion of the delivery member into the well, and a storage device such as a reel to store at least a portion of the delivery member prior to insertion into the well. The system has a motion compensator arranged to compensate for relative motion between the injector and the storage device. The motion compensator optionally is arranged to compensate for relative movement between the injector and the well, and the movement of the motion compensator on the storage device and the motion compensator on the injection head can be coordinated by a motion controller adapted and arranged to measure the movement of the injector and to signal the motion compensator on the storage device to move in accordance with the movement of the injector.