Naturally occurring fractures in hydrocarbon reservoirs may increase the porosity and permeability of the reservoir, and knowledge of the orientation and density of fractures is required to optimize production. In reservoirs having low matrix permeability, areas of high-fracture density may represent “sweet spots” of high permeability, and it is desirable to be able to target such locations for infill drilling. Because fractures show preferred orientations, this may result in significant permeability anisotropy in the reservoir, and it is important for optimum drainage that the separation of producers should be more closely spaced along the direction of minimum permeability than along the direction of maximum permeability. Numerically generated discrete fracture networks are being used increasingly to simulate flow through fractured reservoirs and need to be constrained using quantitative geophysical, geologic, and reservoir engineering data. The hydraulic conductivity of fractures varies strongly with aperture, and the permeability of a naturally fractured reservoir may decline rapidly with decreasing reservoir pressure resulting from production because of the associated increase in effective stress acting on the rock frame. The stress sensitivity of naturally fractured reservoirs is, therefore, also of great interest.