Simple petrophysical models and a sedimentologically interpreted outcrop photograph corresponding to the plane of a ground-penetrating radar (GPR) survey are combined to create models for the simulation of GPR. This makes possible the comparison of GPR field data, synthetic GPR sections, and a lithology image. On the basis of this comparison the usefulness of the method for identifying hydrologically significant lithofacies and the sensitivity of the results to different subsurface conditions may be investigated. In particular, GPR simulations are performed for an outcrop model at three states of water saturation: uniformly drained (uniform residual saturation), nonuniformly saturated, and fully saturated. As predicted by reflection coefficient calculations, comparison among the synthetic simulations highlights the importance of the existing pore water distribution in determining the visibility of lithologic elements in GPR sections. Comparisons of the synthetic GPR sections with the field data show overall agreement, though the occurrence of various observed reflections depends on the presence and distribution of pore water. Conclusions are also drawn about extending outcrop analog-derived results to investigations of real (fully saturated) aquifers. ¿ 2001 American Geophysical Union