We present an engineering model to describe physical adsorption from sub- to supercritical conditions on flat walls and clustering in supercritical fluids using a single temperature-independent parameter for fluid-solid interactions. The fluid-solid potential is superimposed on the Peng-Robinson equation of state, and the configurational energy integral in the inhomogeneous fluid phase is simplified with a local density approximation. This model is capable of quantitative fits over wide pressure and temperature ranges. Model predictions for physical adsorption of pure gases on flat walls are compared with experimental surface excess data, and model predictions for describing the clustering phenomenon are compared with experimental fluorescence spectra.