Due to limitations of cutting picks in terms of rock strength and abrasivity, the application of present day boom type partial-face tunnelling machines is restricted. It seems that the performances of these machines can be improved considerably by hybridizing cutting picks with high pressure water jets. There are many questions that needs to be answered before an excavation machine incorporating high pressure water jets and mechanical tools can be used to excavate rock most efficiently. Amongst these questions are; the selection of optimum water jet pressure and nozzle diameter, the influence of nozzle positioning with respect to mechanical tool e. g. side-off, lead-on, stand-off distances, cutting speed and number of passes of the Jet. The research described in this thesis examines the effect of the above variables on the performance of a hybrid cutting system, together with a comparision of mechanical and hybrid cutting systems in terms of tool forces, yield and specific energies recorded for seven rock types. Small scale qualitative finite element stress analysis was also carried out to analize the stress field around the mechanical tool tip to provide an insight into the mechanics of rock failure under high pressure water jet assisted cutting.