Abstract: A method and reactor system are described for decomposing organic compounds. A gaseous mixture of organic compounds and water, equal to or in excess of stoichiometry, is passed into a first reaction zone having a temperature range between about 200.degree. C. and 1400.degree. C. The first reaction zone has a labyrinthine path which presents organically adsorbent surfaces to the gaseous mixture to provide a residence time in the first reaction zone sufficient to react substantially all of the gaseous organic compounds and the water at high rate. The effluent from the first reaction zone, still with water equal to or in excess of stoichiometry, is then passed to a second reaction zone having a temperature range between about 750.degree. C. and 1820.degree. C. to decompose the organic compounds remaining in the effluent. The first reaction zone is an annulus which is coaxial with and surrounds the second reaction zone. The labyrinthine path is formed by particulate ceramic material.