Low permeability gas sands are a vast future source of natural gas. The main problem in developing this resource is efficiently extracting the gas from the reservoir. The main objectives of this study were to develop new and improved core analysis techniques for measuring petrophysical properties of tight sands and to relate the measured properties to the rock pore structure. The project was subdivided into four major tasks concerned with advanced analysis of core from the Multiwell field experiment. Task I: Advanced core analysis included measurements of porosity (thin section vs. volumetric measurements), Klinkenberg permeability, surface area, and effect of overburden pressure, and pore structure investigations that included x-ray analysis and mineral analysis. Special consideration has been given to origin and types of pore structure. A new concept, the quality of pore space is introduced which is based on the degree to which identifiable pore space is occluded. This work has been greatly aided by application of transmitted light and epifluorescent microscopy. Task II: Gas Flow in Mineralized Fractures. Task III: Chemical Alteration. The control on permeability of the various minerals in MWX cores was investigated by studying the effect of various reagents on permeability and its sensitivity to confining pressure. Treatment ranged from flow of strongly acidic to strongly alkaline solutions; seven reagents were used. Task IV: Effect of Water on Gas Production. Many aspects of the effect of water on the petrophysical properties of tight gas sands were investigated under this task. These included, relative permeability, capillary pressure, imbibition, adsorption, and electrical conductivity. Comparison of the effect of confining pressure on distinctly different transport properties provides a test of the types of pore model appropriate to tight sands. 79 refs., 137 figs., 23 tabs.