The infiltration and the entrapment of hydrocarbon oil on a layer of sediments made up of sand are analyzed in experiments by a device of Darcy. It is shown that the permeability and the porosity of the porous environment are modified. It also discusses the changes in the viscosity of the pollutant after passing on the sand. The analysis of the whole of the experimental results makes it possible to analyze the trapping of the pollutant in the sedimentary layers according to their granulometry. The pollutant which we believe has in its physico-chemical composition of long chains. The impact of the infiltration of the pollutant on the modification of these components will be discussed.