The desorption profiles of various organics from soil and activated carbon using dense liquid and supercritical carbon dioxide were modeled. The model accounts for effective diffusion of the organics in the solid pores, axial dispersion in the fluid phase, and external mass transfer to the fluid phase from the particle surface. This model, involving partial differential equations, is solved using the orthogonal collocation on finite elements. The model is able to predict the experimental data quite well without any adjustable parameters. The importance of each parameter depended on the system, although adsorption equilibrium and the effective pore diffusion of the organic were the most significant parameters in all the systems investigated.