For reflected-wave phenomena in both seismology and ground-penetrating radar (GPR), the amplitudes of the reflected waves depend on the incidence angles and the physical properties of the media above and below an interface. Amplitude variation with offset (AVO) analysis employs knowledge of reflected-wave phenomena to constrain the physical properties of two media at an interface. Ostrander (1984) demonstrated that AVO analysis can be used on seismic reflection data in certain instances to obtain information about the subsurface not revealed by traveltime-offset relationships (i.e., traditional seismic cross sections). Quantifiable information about the physical properties of the subsurface may then be extracted. AVO analysis, proven for a decade to work well in reflection seismology, may be useful in near-surface hydrogeological situations when applied carefully to GPR data to better constrain the presence or absence of nonaqueous phase liquid contaminants (NAPLs) in the subsurface. ¿ 1998 American Geophysical Union