The effects of selective microbial activity on hydrocarbon accelerants have been examined both in vitro and in simulated arson residues. Two groups of Pseudomonas species that assimilate components of common petroleum based accelerants have been found; one species metabolizes only aromatic hydrocarbons, the other only aliphatics. The kinetics of hydrocarbon metabolism are discussed and gas chromatographic profiles of two common accelerants that have been subjected to microbial attack are presented. Some implications and recommendations for arson investigation are discussed.