Downhole pump insert the whole pumping mechanism into the well. In modern installations, an Electrical Submerged Pump (ESP) is inserted into the well. Here the whole assembly consisting of a long narrow motor and a multi phase pump, such as a PCP (progressive cavity pump) or centrifugal pump, hangs by an electrical cable with tension members down the tubing. Ill: Wikipedia.org Installations down to 3.7 km with power up to 750 kW have been installed. At these depths and power ratings, Medium Voltage drives (up to 5kV) must be used. ESPs works in deep reservoirs, but lifetime is sensitive to contaminants such as sand, and efficiency is sensitive to GOR (Gas Oil Ratio) where gas over 10% dramatically lowers efficiency.