Nearly 20 years of research and field testing has resulted in the development of Hydratherm (TM) 's hybrid drilling system, Which uses ultra-high pressure (UHP) drilling fluid jets and/or a variable thermal spallation gas jet. The gas jet subjects the host rock to pulsed heat fluxes at temperatures ranging from 200 degrees C to 1,100 degrees C, producing thermal expansion and strength reduction of the rock-forming minerals. The UHP jets then quench, cut and erode the rock momentarily after heating. The combined mechanisms enable ultra-fast rock penetration (20 - 50 m/hr in hard rock) by means of spallation, erosion, fracturing, chipping and cutting. This technology should bring about exciting developments in heavy oil recovery, tar sand and oil shale exploitation, as well as having wider applications in mining, tunnelling and geothermal energy recovery ("HDR heat mining").