Nonaqueous phase liquids (NAPLs) are a common source of contamination at polluted groundwater sites, where they frequently remain trapped within the pore space at residual saturation and reduce the permeability of the medium to aqueous phase flow. The model presented in a companion paper <Imhoff and Miller, this issue> suggested that when fluid flow is imposed on such a system, the aqueous phase may interact with dissolution-induced permeability changes, and lead to fingered patterns. In this investigation, a two-dimensional flow cell was used to study the effects of porous medium structure, Darcy flux, initial residual NAPL saturation, median particle diameter, gravity, and NAPL composition on dissolution fingering. Fingering occurred when two conditions were met: (1) 11 to 80 e-fold times had elapsed, where e-fold time is the time required for the instability to grow by a factor e and was predicted from the linear stability analysis in the companion paper; and (2) the length of the dissolution front before finger development was smaller than the zone of NAPL residual. Where fingers formed, finger structure was similar and showed no systematic variation within the parameters investigated. Observed finger wavelengths compared well with model predictions. A single experiment in a three-dimensional cell, 1 m long, demonstrated that fingers can grow to at least 30 cm in length. When experimental observations in this cell were compared with predictions of NAPL dissolution based on models that did not include fingering, the measurements of changing NAPL saturation differed significantly from model predictions. ¿ American Geophysical Union 1996