Determination of the equilibrium aqueous concentration and the distribution coefficients, K, in soil samples containing oil residuals of different age, was carried out using an organic co-solvent (methanol). It was found that the solvophobic theory could be applied for the interpretation of results. The behavior of the residuals turned out to be dependent on the co-solvent fraction and the age of the oil spill. The values of K vary between 900 (l kg(-1)) and 2,900 (l kg(-1)) showing a general and marked increase for residues of increasing age. The determined parameters are useful for the modeling of environmental impact on polluted soils.