A simple two-vessel fluidized-bed oil shale retorting process is considered. Fresh shale is pyrolyzed in a fluidized-bed retort, and the residual char on the shale is burned in a fluidized-bed combustor to provide process heat. Heat is transferred to the retort by recirculating solids between the combustor and the retort. The proposed process is analogous to a fluid catalytic-cracking plant. Such plants are currently in operation with combustor units up to 20 m in diameter. It is estimated that a combustor of this size could supply sufficient heat to retort the amount of shale necessary to produce about 100,000 b/d of shale oil. This paper is concerned with an evaluation of the overall energy balance and the impact of the decomposition of calcite (CaCO/sub 3/) minerals in the shale on the energy balance of such a retorting arrangement. The shale deposits in the Green River formation generally contain substantial amounts of carbonate minerals, and the complete decomposition of calcite, CaCO/sub 3/ = CaO CO/sub 2/ ..delta..H/sup 0/ = 1.832 x 10/sup 8/ J/kgmole(1) will require a significant fraction of the heat of combustion of the char. The results of this study showed that, for certain operating conditions, significant amounts of calcite will decompose and that the energy requirement for decomposition will affect the reactor temperatures. The presence of calcium oxide in the retort will also alter pyrolysis product yields. Some experimental data on pyrolysis product yields from fluidized-bed retorting of oil shale in the presence of CaO are briefly mentioned. The ASPEN process simulator and economic evaluation system was used to develop the computer model of this recirculating solids process.