In this paper a mathematical model and numerical investigations on dynamic water/oil contact (WOC) in a reservoir with active bottom waters are addressed. An original analytical solution describing the theoretical shape of the dynamic oil-water contact in the reservoir is presented and compared with some results of numerical simulations made by a commercial flow-simulator It is shown that both water and oil may be produced simultaneously but selectively from their respective zones. This allows a theoretical control of the dynamic WOC by the water flow rate. Consequently, an increased amount of oil can be produced along with water depending on the well completion interval in relation to the oil/water contact in the reservoir. This shows the possibility of all "in situ" separation concept. The advantage of such a separate production of water and oil is to prevent the mixing oil with water within the pump and tubing.