Accurate data to understand the migration and entrapment of nonaqueous-phase liquids (NAPLs) in heterogeneous formations are presently lacking. A series of well-controlled laboratory experiments were conducted to investigate the infiltration and subsequent immobilization of dense NAPLs in saturated heterogeneous media. The focus of this first study was the development of a special experimental methodology for measuring the dynamic evolution of a NAPL plume in space and time. To demonstrate the method, a reference case of a two-layered formation consisting of two homogeneous sands separated by a dipping interface is presented. The dipping formation in the reference case allows the study of NAPL behavior at texture interfaces under the influence of both capillary and gravitational forces. The NAPL-saturation measurement methodology, based on a multiple-energy x-ray attenuation technique, correctly captured the known injected NAPL volume as well as the general spreading and entrapment behavior in space and time. Time-continuous measurements of NAPL saturations allow the study of the history dependence of entrapped saturations. The Land model predicted the observed trend in the entrapment behavior well. The entrapment architecture was parameterized using spatial moments and moments of mass distribution at different saturations. The general features of the NAPL architecture were successfully characterized by a simultaneous interpretation of these moments, while the domination of discontinuous or continuous NAPL was captured by the ganglia/pool ratio.