When a direct current electric field is applied to a wet porous medium polluted by hydrocarbons or by ionic species, the aqueous phase is displaced by electro-osmosis in the pores and the ions migrate towards the electrodes. As a result, among other things, the value of the local pH at the interfaces between water, oil and solid is changed, as well as the electric conductivity of the medium: the ionic strength is increased towards each electrode and decreased between them. These mechanisms result in release of the oil droplets which block the capillary tubes of the medium, either by mechanical action (movement of the water), or by chemical action (change of the surface tension at the interfaces). Additionally, the electromigration of ions through the medium can decrease the contamination level of aquifers by charged chemical species. These mechanisms were identified on polluted chalk cores, sandstone blocks, or sands. The role of the various parameters was analysed: the direction of the current is unsensitive, the adding of surfactants increases the flow and a sequence of currents plus water-drives with small gradient increases the oil recovery. The use of electric currents for improving the cleansing of aquifers polluted by hydrocarbons can be considered together with the more usual pumping in ordinary wells. The method can also be used for cleansing of aquifers polluted by ionic species.