We studied the dissolution of nonaqueous phase liquids (NAPLs) at residual saturation in two-dimensional systems using physical and numerical experiments. In all cases, preferential dissolution pathways developed in the NAPL-contaminated regions. A permeability feedback mechanism led to the formation of centimeter-scale dissolution fingers in homogeneous porous media, while fingers up to 1 order of magnitude wider formed in media with heterogeneous distributions of intrinsic permeability k, when σ2(lnk) was large. The structure of the interface between the NAPL-contaminated and NAPL-free regions was examined as dissolution progressed. In all cases the interface was a self-affine fractal. The scaling relationship of Family and Vicsek <1985> fitted the interface data from the numerical simulations reasonably well.