Abstract: A high-speed fluid/mechanical jet erosion system utilizing a high-velocity, jet stream discharged contiguous the surface to be cut. The jet stream is developed from a single plenum flow system adapted to merge and enhance the erosive high-speed fluid jet characteristics of fluid with cavitational collapse erosion. The system further includes a tapered drill bit housing, with mechanical cutters therealong which places a generally axially centered, exiting jet immediately against the target formation, providing maximum mechanical and fluid energy transfer to the formation.