A mathematical model has been developed for vertical forward combustion retorting of oil shale. The model is based on fundamental material balances for solid and gas phases components and energy balances for the solid-liquid and gas phases. In addition to the decomposition reactions of kerogen and inorganic carbonates and the combustion of recycle gas and oil. For known operating conditions like air and recycle gas rate, Fischer assay of oil shale, void fraction and particles size in the retort, the model can be employed to predict the oil recovery, retorting advance rate, average peak temperature in the retort, and composition of recycle gas and spent shale. Computed results from the model show reasonable agreement with the experimental results of the Laramie Energy Research Center (LERC) 150 ton (136,200 kg) capacity batch retort.