Evaluation of the fluid content in deep earth reservoirs or of fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting. The processing of these seismic data has involved meticulous care in determining the changes in reflected seismic amplitude as the point of observation for the received signals at the earth's surface is moved away from the seismic source (Ostrander, 1984). The now commonly used method called AVO (for Amplitude Versus Offset) is based on theories of fluid-saturated and partially saturated rocks that have been available since the 1950's. Here we present a new synthesis of the same physical concepts that uses some of the same data as AVO (compressional wave velocities) together with some different data (shear wave velocities) in a scheme that is much simpler to understand and apply, yet yields the desired information about porosity and fluid saturation. The method is designed especially for near surface applications and for use with crosswell and VSP data, but it can also be applied to reflection seismic data assuming that reliable interval velocities are available. Since the new method does not require hard-to-obtain wave amplitude information, it can be used for a wider range of seismic source-receiver configurations, including crosswell seismic transmission tomography (well-to-well), vertical seismic profiling (well-to-surface), as well as seismic reflection profiling (surface-to-surface), since reflection data can be used but are not a necessity.