Seismic imaging of the subsurface has been very successful in delineating the relatively gross structural features that are significant in oil and gas exploration. Since conventional seismic exploration imaging (frequency range 10--100 Hz) can only resolve subsurface features having dimensions or thickness greater than about 50 feet, it has limited direct application to detailed reservoir characterization. Experiments have indicated that, although more demanding in instrumentation and field efforts, frequencies in the range of 500--2500 Hz can be used in downhole seismic applications. Measurements in this high-frequency range may allow a detailed determination of acoustic parameters related to permeability, porosity, temperature, etc., and may provide spatial imaging of the reservoir lithology and tectonic characteristics to an unprecedented degree. This quality of high-resolution seismic imaging can be used for planning the overall development of oil and gas fields, monitoring of secondary and tertiary recovery projects in mature oil fields, monitoring of fire or stream flood projects in tar sands and heavy oils, and monitoring of oil shale processing techniques developed in situ production. One seismic imaging technique that has high potential for application in reservoir delineation is inverse vertical seismic profiling (VSP) in which a seismic source is positioned at different depths in the well and the detectors are carefully planted near the surface. Inverse VSP measurements in the frequency range of 500--2500 Hz can image a significant volume of the subsurface immediately surrounding a well bore with a resolution in the order of 5--10 feet. With this degree of spatial resolution, petroleum engineers will have the necessary information for accurately designing EOR projects, fire, floods, etc.