(57) Ash-slagging fixed bed gasification of carbonaceous materials with steam and oxygen is effected by substituting at least a portion of the steam with an aqueous liquor. The liquor may be water per se eg. boiler-feed water or an effluent liquor comprised of condensed organic compounds and unreacted steam and solubilised salts which liquor is obtained by treating the product gas. Although oxygen consumption is slightly increased, the economic effect is offset by not having to expend energy in steam raising.