When the so called "porous unsaturated medium", that' s the vertical subsoil section between both the ground and water-table level, is interested by a hydrocarbons spill, theproblem to evaluate the pollution becomes difficult: considering, essentially, the natural coesistence in it of two fluids, air and water, and the interactions between them. The problems tend to increase when a third fluid, the pollutant, immiscible with water, is introduced into the medium: a three-phases flow, which presents several analogies with the flow conditions present in an oil-reservoir, will be established. In such a situation, it would be very useful to handle the matter by the commonly used parameters in the oil reservoirs studies such as: residual saturation, relative permeability, phases mobility, to derive a first semiguantitative estimation of the pollution.
The subsoil pollution from hydrocarbons agents is one of the worldwide more diffused causes of contamination: such events are generally referable to two main effects: accidental (oil pipelinebreakdowns, e.g.), and continuous (underground tanks breaks, industrial plants leakages, e.g.)