Methods and apparatus employing inert gases injected into the lower level of sloping underground oil-bearing formations as a driving mechanism and water injected into the upper level of the formations as a gas blocking mechanism for increasing and extending the production of oil from underground formations is described. An oil production system to produce oil from a viscous reservoir is provided including at least one production well, a fluid injection well, and a heating system functionally associated with the at least one production well, the heating system having at least one electrical heating well adapted to direct power from a power supply at surface to the reservoir to heat the reservoir. Hydraulically-operated crude oil pumps are also provided.