Abstract: Crushed oil shale is subjected to eduction in a solids-upflow or -downflow retort in contact with a preheated counter-currently flowing eduction gas comprising a recycled portion of the retort make gases. The problem of shale particle agglomeration is avoided by correlating the eduction gas flow rate and temperature so as to insure that the 750.degree.-850.degree. F shale temperature interval in the retort is maintained at a level sufficiently high in the retort that the total shale, or "rock" pressure bearing down on said interval is insufficient to bring about agglomeration. It is found that the problem of agglomeration is critical to the 750.degree.-850.degree. F temperature range, and that there is a definite correlation between the oil assay of the raw shale and the permissible rock pressure which the shale particles in this temperature range can withstand without undergoing agglomeration. Provision is made for shifting the 750.degree.-850.degree. F zone upwardly or downwardly in the retort.