Abstract: A mechanical oscillator which employs unbalanced rotors is coupled to the top end of a drill string which has become stuck in a bore hole. The rotors are driven at a rotation speed such as to generate high level energy at a sonic frequency, this energy being coupled to the drill string. A low impedance load for the oscillator and the top of the drill string is created by supporting the oscillator from the support structure, which may comprise a derrick or the like, by means of a highly elastic support which may include elastomeric stretch bands, springs or other elastomeric support having a linear constant spring rate. In addition, hydraulic cylinders which may be servo driven are used to keep the drive motors for the oscillators in one place as the oscillator structure vibrates. The oscillators are driven at a high energy level to effect high displacement of the top of the drill string which presents a low impedance load to this energy in view of the highly elastic support provided.