"The study of various proposals for retorting oil shale has resulted in the recognition of the existence of certain fundamental relationships which must be considered when evaluating oil-shale retorting processes. Retorting-plant designs frequently are predicated on heat transfer considerations alone. Examination for a limiting mass shale rate, expressed as pounds per hour per square foot, is often overlooked. Such a limitation on the allowable mass shale rate appears to exist for the internal-combustion type of retort . Based on factors to be discussed later, a much higher mass shale rate should be permissible for retorts operating on the carrier-gas recirculation principle. Oil-shale retorting processes may be classified into five broad categories according to the nature of the method used for the introduction of heat to the shale: Class I - Retorting by heat transfer through a wall to the shale. Class II - Retorting by heat transfer from flue gas generated by combustion of shale within the retorting vessel . Class III - Retorting by heat transfer from an externally boated carrier fluid (gas or liquid) recycled through the retorting bed. Class IV - Retorting by heat transfer from externally heated solids recycled through the retorting bed. Class V - Retorting by electrical methods such as induction, radiant, or resonant heating. The emphasis of engineering research to date has been directed toward the development of gas-to-solids shale-retorting processes. The two possibilities for gas-to-solids heating are by internal combustion (Class II) and by a heat-carrying medium (Class III),wherein recirculated carrier gas is heated through the use of auxiliary equipment outside the retort itself. The first part of this report will be concerned with internal combustion retorting, while the second will touch upon the carrier-gas retorting principle."