Abstract: Apparatus for electrically generating hydraulic shock waves in a fluid bearing formation (14) of a bore hole (10) including a tool (16) having an upper electrode (42) and a lower electrode (46) forming a spark gap therebetween. The tool (16) has an upper end portion (40) comprised of a plurality of sections (40A-40E) threaded to each other in end to end relation and an armored electrical cable (18) having an outer metal sheath (34) is anchored to the uppermost section (40A). The tool (16) is particularly adapted for fitting within a casing having a four inch diameter and the electrodes (42,46) have diverging planar end surface portions (84) coated with tungsten carbide to provide wear resistant surfaces.