Abstract: Low heating value liquid hydrocarbonaceous and/or solid carbonaceous hazardous waste materials from the production, refining and marketing of petroleum products are destroyed without contaminating the environment while simultaneously gaseous mixtures comprising H.sub.2 +CO i.e. synthesis gas, reducing gas, or fuel gas are produced. From about 0.3 to 2.0 wt. % of an anionic surface active dispersant and water (if needed) are mixed with the hazardous waste material to produce a first aqueous mixture. A comminuted solid carbonaceous fuel i.e. coal, petroleum coke is mixed with water and from about 0.02 to 1.00 wt. % of the dispersant to produce a second stable pumpable aqueous slurry. The first and second aqueous slurries are mixed together to produce a stable pumpable final blend aqueous slurry which is reacted in a partial oxidation gas generator as the feedstock.