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Methods of improvement in the performance of mechanical rock cutting systems are continually being sought. One area being investigated is combining mechanical rock cutting tools with water jets. In this ‘hybrid’ arrangement, the mass breakage mechanism of a rolling disc cutter or drag pick is coupled with the concentrated energy medium of a high pressure water jet. Research has indicated that the resultant improvements in performance of mechanical cutting tools could be due to the cutting of the rock surface through fracture and erosion thereby ameliorating the rock breakage process of the mechanical cutting tool. Damage by a water jet has been observed even in rock of high strength. This paper outlines a study on the sole use of water jets in cutting rock and the effects of changes in the principal variables of a water jet. An understanding of the characteristics and the relative importance of any changes in these variables is necessary to optimise the cutting performance of a hybrid system in terms of advance rate and energy expenditure. The variables considered in the study included nozzle diameter, water pressure, traversing speed and multiple passes of a water jet. Within the range of values studied for each variable, a change in water pressure was found to have the greatest impact on the level of surface damage in rock. Traversing speed, and to a lesser extent nozzle diameter, were also found to alter the magnitude of surface damage in rock.