A process for recovering hydrocarbon products from a body of fragmented or rubblized oil shale. The process includes initiating a combustion zone adjacent the lower end of a body of oil shale and using the thermal energy therefrom for volatilizing the shale oil from the oil shale above the combustion front. Improved recovery of hydrocarbon products is realized by refluxing the heavier fractions in the volatilized shale oil. The heavier fractions are refluxed by condensing the heavier fractions and allowing the resulting condensate to flow downwardly toward the combustion front. Thermal energy from the combustion zone cracks the condensate producing additional lower molecular weight fractions and a carbonaceous residue. The carbonaceous residue is burned in the combustion front to supply the thermal energy. The temperature of the combustion front is maintained by regulating input of oxygen to the combustion zone. The process also includes sweeping the volatilized products from the rubblized oil shale with a noncombustible gas. The flow rate of sweep gas is also controlled to regulate the temperature of the combustion front. The recovered products can be enriched with hydrogen by using water vapor as part of the noncombustible sweep gas and cracking the water vapor with the hot carbon in the combustion front to produce hydrogen and an oxide of carbon.