This report summarizes the research and activities of the LLL Gas Stimulation Program during the final quarter of FY 1979. We have continued our theoretical model development and application. Analyses of frictional interfaces, with similar materials on both sides of the interface, show that frictional slippage along the interface tends to draw a pressurized fracture toward the interface. Increasing friction along the interface changes the position at which the pressurized fracture is affected by the interface. The dynamic effects of propagation near a well-bonded interface between two dissimilar materials are not significantly modified by the velocity of the dynamically propagating fracture for fracture by velocities below the body wave speeds. We have shown the pressure evaluation of the fracturing fluid in a crack. One notable feature of these calculations is the rather sudden increase in fluid pressure at the fracture tip just after the fluid reaches it. Frictional interface experiments using various lubricants on the interface show distinct changes in the frictional coefficient; however, these tests indicate that the interface must support about 350 psi (24 GPa) in shear (frictional) stress before a fracture will penetrate the interface. Our studies of the occurrence and mechanics of natural fractures in the western reservoirs show that in a relaxed tectonic setting, one principal stress is most often nearly vertical and the other two are horizontal. Local stresses that control small fractures such as joints may be different from, although compatible with, the regional stresses. Fractures are controlled by the physical environment, the stresses, and changes in stresses due to burial and uplift. Jointing frequency is greater in weak and thinly bedded rocks and is directly related to the intensity of folding.