Abstract: A method for preparing a shale oil deposit for in situ retorting includes providing a drilling and process control level above the deposit with a substantial thickness of personnel isolating and protecting formation between the deposit and the level, providing a collecting and pumping level below the deposit with a substantial thickness of personel isolating and protecting formation between that level and the deposit, and excavation providing voids affording fragmentation of shale in the retorting zones reached from the collecting level. The shale excavated to provide the voids is transported through access risers to the collecting level; closures serving as sumps and protective gratings for the sumps are installed in the upper ends of the risers. Introduction of combustion gases from the control level is accomplished through drill holes provided for this purpose, some of the drill holes also being provided with control or detecting devices.