Our paper deals with the diffusive model of hydrocarbon migration in the soil. To assess the risk of groundwater contamination by hydrocarbons migrating in the soil, a mathematical model had been applied. Incorporation of diffusion into the equation of mass transport enables the description of hydrocarbon transport deep into the soil profile. The biodegradation equation makes it possible to consider the effect of microorganisms upon reduction of hydrocarbon concentrations, especially oil fractions. To verify a theoretical model, a series of experiments on a so-called soil filter were carried out. Finally, a theoretical model was used to determine the parameters that shows the behavior of different contaminants through soil.