Abstract: New and improved techniques, systems and equipment for the practical underground mining of petroleum from both virgin and depleted oil fields under certain geological conditions, are described. A method of drilling relatively small diameter, drainage-type oil wells using a fluid and cutting control assembly from within an access underground drilled tunnel, is provided. The fluid and cutting control assembly facilitates the safe underground drilling and installation of the small diameter, drainage-type oil wells which can be operated either under the natural pressures occurring in the geological strata, as gravity drain wells or by suitable secondary treatment measures artificially pressurized to faciliate drainage of oil from oil bearing strata into which such wells are drilled.