A process and apparatus for gasification of organic materials (typically incorporated in domestic and industrial wastes, including auto shredder residues) to produce useful synthesis gas (with a major content CO and H.sub.2) with effectively non-toxic ash residue by means of at least one continuously operated burner, preferably stoichiometrically balanced (1:2 for natural gas/oxygen) at least at startup and shut down (optionally with some excess of oxygen, usually under steady-state conditions, such as at a ratio of 1:4 or higher, especially if the charge has well over 18% water content), directed into a primary single stage reaction zone (through an opening in common with the effluent product gas discharged therefrom such as to assure intimate contact therebetween), which zone contains a tumbling charge in a rotating barrel-shaped horizontal reactor thus heated to from about 650.degree. to about 800.degree. C. (below the incipient fusion temperature of the charge) and controlled to remain in such temperature range (by adjustment of the burner volume and fuel-to-oxygen ratio for any given charge) resulting in thermally cracking and gasifying the organic materials in the charge and reacting the complex hydrocarbons and gas evolved (1) normally with the CO.sub.2 and H.sub.2 O derived from burner combustion of a fuel and oxygen-containing gas at a high flame temperature, typically 2500.degree. to 3000.degree. C., (2) with excess oxygen, and/or (3) partially with H.sub.2 O or CO.sub.2 otherwise added to or, present in, the charge.