a method and apparatus is disclosed for retorting particulate solid materials , particularly hydrocarbon - containing materials such as oil shale , oil sands , tar sands , coal shale , coal tailings , and the like , for the recovery of a volatile constituent such as oil or gas . a rotary retorting apparatus is employed which consists of a cylindrical drum , or other similar regularly shaped chamber , with a substantially horizontal axis of rotation and having multiple compartments for retorting and combustion and , optionally , spent solids cooling . the apparatus further includes solids transport chutes for forward and backward circulation of solids , arranged for the intercompartmental transfer of solids with the capability of additions at one or more points in each compartment . employing the method and apparatus , particulate solids feedstock is heated by recycled spent solids material to remove the volatile constituent of the feedstock in the retort section . another feature of the invention employs direct solids - to - gas contact established by lifting and cascading reacting solids through hot gas streams such that throughput , high thermal efficiency , low energy input , among other advantages , are obtained in producing high yields of volatile product . in particular , high oil yields and gas yields are obtained when processing oil shale , but with low sulfur oxides , nitrogen oxides in the flue gases and reduced hydrogen sulfide in the retort gases .