The report, one of several data summary reports on the environmental aspects and pollutants specific to coal gasification, addresses characteristics of solid wastes (ash and cyclone dust) and by-product tars and oils analyzed in nine EPA source tests and evaluation studies and limited other data. Objectives of the report were to compile and summarize solid waste properties and identify behavioral trends. Results of this data compilation showed that gasifier ash and cyclone dust are non-hazardous under RCRA and negative according to selected bioassays. However, ash compositions differed with different processes, operating conditions, and feedstocks. Tars and oils are more likely to pose environmental problems due to detectable concentrations of polynuclear aromatic compounds, other toxic and carcinogenic organic compounds, and entrained trace elements. However, high heating values of tars and oils make them candidates for use as fuels if the organic residues are treated properly. Engineering and leaching properties of gasifier solid wastes are not sufficiently defined to allow a good evaluation of disposal alternatives.