An improved method of disposing of radioactive or hazardous liquid hydrocarbon compositions comprises placing the liquid hydrocarbons in a container and adding an organic ammonium montmorillonite in ratios of between about 1:2 and 3:1, by volume, respectively. The organic ammonium montmorillonite has at least 10 carbon atoms. A polar organic compound having between 1 and about 10 carbon atoms is also preferably added with the montmorillonite. Where the liquid waste material includes 5% or more of water in addition to the liquid hydrocarbon a minus 200 mesh sodium montmorillonite is also preferably added.