The objective of this investigation was to determine the physical and geotechnical properties and composition of spent oil shale by the paraho and tosco processes. The program was divided into three categories: physical properties, engineering properties, and compositional and durability characteristics. The physical properties tests consisted of typical classification tests for identifying and comparing the retorted shales with other materials. The engineering characterization investigated compaction, consolidation, shear strength, self-cementing tendencies, particle breakage and abrasion, dynamic properties, and earthquake resistance. Compositional tests consisted of x-ray diffraction, petrographic and scanning electron microscopy, and differential thermal and chemical analyses.