Abstract: A process is disclosed for contacting at least two solids and a fluid, particularly for retorting and/or gasification of solid carbonaceous materials such as coal, coke, shale or tar sands by introducing a solid heat-transfer material into an upper portion of a treatment or contacting zone and a solid carbonaceous material into a lower portion of the treatment or contacting zone. The solid heat carrier is fluidized by an upflowing gas and moves downwardly, while the solid carbonaceous materials are entrained and move upwardly. The fluidizing gas may be inert or reactive. Substantially countercurrent plug flow of the two solids in the treatment or contacting zone is maintained by including means for preventing back mixing, such as a packing material filling the treatment or contacting zone.