The investigation of oil shale pyrolysis in the experimental retorting system by solid heat carrier (silica sand) was conducted. Modeling of the heat and mass transfer processes in the retorting system was performed with use of simplified mathematical model. It was shown that the radiation heat exchange plays the main role in the heat transfer between oil shale particles and solid heat carrier under the conditions of volatiles release. The maximum yield of the shale oil amounts to 73% at temperature of experiment of 560 degrees C, which exceeds the data obtained in the Fisher assay on 20%. The conditions that lead to increase in maximum yield of shale oil in the industrial UTT units with the rotary drum reactor were ascertained. They are mainly associated with a decrease in the solid heat carrier (ash) temperature, which leads to the inhibition of secondary reactions between ash and the acidic compounds of the shale oil. (C) 2016 Elsevier B.V. All rights reserved.