Department of Energy supported research conducted in the tight gas sands of the Piceance, Uintah, and Green River Basins of Colorado, Utah, and Wyoming directed toward evaluating massive hydraulic fracturing (MHF) for increasing natural gas production. Research at Bartlesville Energy Technology Center supporting the Western Gas Sands Project consists of examining potential areas of formation damage by MHF fluids and proppants. Fractures produced by the MHF process are propped open by placement of particulate materials creating zones of high permeability and porosity. In this research, high permeability fractures were simulated by placing 40/60 mesh sand proppant between core halves, and subjecting the cores to increasing overburden pressure. As the proppant was crushed, the resultant particles were transported through the propped fracture by frac fluids. Mean, mode, and number per unit volume of the produced particle size distributions were pleasured and related to overburden pressure. The effects of particle retention, when pumping similar particle distributions through the propped fracture, were detected by a pressure change across the core. Measured changes in the filtration efficiency, conductivity, and threshold plugging pressure of 'the propped fracture showed significant particle trapping within the porous media. Pressure versus time plots indicate successive pore plugging and particle breakthrough until the fracture is ultimately plugged.