 Recovery factor during the primary recovery stage is typically 5-15%.While the underground pressure in the oil reservoir is sufficient to force the oil (along with some associated gas) to the surface, all that is necessary is to place a complex arrangement of valves (the Christmas tree) on the well head to connect the well to a pipeline network for storage and processing.Sometimes pumps, such as beam pumps and electrical submersible pumps (ESPs), are used to bring the oil to the surface; these are known as artificial lifting mechanisms.