A gravity feed inclined retort apparatus provides for a distillation process in which oil is removed from shale ore in the inclined portion of the retort, and the gaseous oil is removed to a vapor condenser/separator in which the vapor is condensed into the product oil. The retorted shale is fed onto a continuous chain stoker, or other similar conveying device, where the coke portion of the retorted shale is burned as fuel for the retort. Hot gases from the combustion zone where air is directed through the burning coke are used to preheat the shale ore above the dew point of the oil, through a heat exchange plate; and the hot gases then flow through the shale ore in the retort chamber, picking up the oil vapors from the heated shale, and carrying this oil-filled gas into a vapor condenser/separator. Some of the oil vapors are also condensed onto cooled side walls extending along the retort chamber and this condensed oil flows into oil collection gutters. The retort chamber is slightly enlarged along its length in the downward direction of shale movement to preclude clinkering and blockage of the continuous operation. The retort chamber is oriented at approximately 45.degree. from the horizontal for gravity feed; and the heat exchange plate is raised at its center and pitched at an angle of about 15.degree. relative to a line extending across its width for free shale movement down the expanding retort chamber.