The report gives results of an examination, including mutagenic screening, of the chemical composition of residual fuel oils and their column chromatography pre-fractions. A degree of correlation between composition and mutagenicity has been achieved. Radionuclide data has been obtained. A novel sample processing technique has been developed for solvent partitioning followed by column chromatography. It concentrates mutagenic factors into fractions that retain their chemical class distinctions but eliminate sample components that are not of environmental concern. An as-received residual fuel oil is either non-mutagenic or only weakly mutagenic. In this respect, residual oils would not be considered environmental hazards. A residual oil can be fractionated so that fractions will be mutagenic. Some fractions from some oil samples can be strongly mutagenic. (To determine if physical or chemical processes in use or in the environment could concentrate or create mutagenicity is beyond the scope of this work.)