A computational model is used to predict the propagation of gas-driven fractures emanating from a pressurized borehole. In some calculations, it is presumed that the borehole pressurization occurs instantaneously, as in explosively driven applications. In other examples, the rate of pressurization is controlled by a pressure-dependent burn model, as appropriate for propellant driven applications. In all cases, the decay of borehole pressure is calculated from the rate of gas flow into the fractures. The gas velocity and the pressure distribution are determined from a one-dimensional analysis of heat, mass, and momentum transport along the fractures, taking into account the space-wise and time-wise variations in fracture opening displacements, as well as the seepage losses and heat losses into the walls. Laminar and turbulent friction are based on the customary friction-factor methodology. Opening displacements and stress intensity are evaluated using quasi-steady integral representations from linear elastic fracture mechanics. The fracture speed, gas-pressure distribution, opening displacements, and borehole pressure are evolved in a fully coupled time-marching fashion such that all of the transport equations are satisfied and the stress intensity at the leading edge of the fracture is maintained at the critical value. Calculations of peak pressure, pressure-decay time, and fracture extent are in good agreement with several sets of data from the propellant-driven field experiments conducted by Sandia National Laboratories in the tunnel-bed tuffs at the Nevada Test Site. Parameter studies illustrate the effects of rock permeability, fracture surface roughness, heat transfer, in situ stress, borehole size, propellant characteristics and loading density, and multiplicity of fractures.