A process and gas generator is disclosed for generating by dry distillation of solids and gasification of solids, a fuel gas substantially free of condensable dry distillation volatiles which would interfere with the intended use of the gas, e.g. for powering an internal combustion engine. To achieve this, solids beds in distinct dry distillation and gasification zones are maintained under conditions favouring thermal cracking of condensable (tar) volatiles in the hot regions of both zones. For optimal control of these conditions these zones are physically separated by internals within a single reactor vessel and optionally by performing part of the dry distillation (pyrolysis) in a separate reactor vessel, in which case pyrolysis volatiles are fed in counter-current to the dry distillation bed, withdrawn from the top thereof and fed into and through the embers bed of the gasification zone. Thermal cracking of pyrolysis volatiles is prolonged and intensified by the manner in which these volatiles are conducted in intimate contact through the embers bed of the gasification zone in co-current therewith. The embers bed is guided along a progressively constricting pathway, which controls the rate of travel of and the period of residence of the solids bed in the process and generator.