The flow of oil and water is introduced to the tank and distributed in a homogeneous way across the whole cross-section. A conical receiver is located beneath the entry zone for the collection of any sediment or sludge present in the water. The effluent water passes through the lamellar pack due to gravity (from the top to the bottom) with uniform velocity and flowrate inside every channel. During the downward motion the single oil particles, which have a lower density than that of the water, tend to rise to the surface under the force of gravitational upthrust. At this point the particle is separated from the transport fluid and starts to rise to the top thanks to both the slope of the channels and the velocity of water, that is almost zero in the zone close to the wetted perimeter. Once they reach the surface, the oil particles are collected in the central area of the tank, above the lamellar pack, from where they are extracted with an oil-skimmer. The oil-free water, returned from underneath the lamellar pack, reaches the free surface on the side opposite of that of the inlet feed and from there is channelled outwards, to a drain or to any subsequent treatment.