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. Also described is an inert gas oil production system comprising an exhaust gas processing system, a well inert gas and water injection system, an oil production well system, and a fuel gas generator. A hydraulically operated crude oil pump is also described.