In recent years there has been a growing interest in applying proppant free fracturing technique to stimulate tight to ultra tight gas reservoirs. The permeability enhancement mechanism for proppant free fracture stimulation has, in the HDR geothermal industry, been long recognised as shear dilation induced by elevated fluid pressure. Passive micro seismic monitoring technique has been well established in the HDR geothermal industry for imaging growth and geometry of reservoirs created by proppant free stimulation. Both field evidence from seismic monitoring and 3D stochastic stimulation modelling show clearly the volumetric nature of the stimulated rock mass with the proppant free stimulation technology. The detailed reservoir geometry, however, is complex due to interaction of natural fractures and in-situ stress regimes, and may be controlled either by dominant fracture sets or in-situ stresses. There exists a threshold stimulation fluid pressure above which permeability of stimulated fractures increases rapidly with increase in fluid pressure. The threshold pressure is inversely related to the deviatoric stresses. In regions with strong deviatoric stresses such as in Central Australia, the threshold stimulation pressure is expected to be low. Thus, creation of a large volume of reservoir by relatively low stimulation pressure could make the proppant free stimulation a viable alternative to conventional massive hydraulic stimulation from both technical and economical stand point.