Biotransformation and biodegradation of polycyclic aromatic hydrocarbons by the subsurface autochthonous microflora collected from an abandoned petroleum refinery site was investigated. In addition, the inoculation of a commercially available blend of bacterial cultures, with known ability to degrade polycyclic aromatics, was evaluated. This supplemental addition of select microorganisms has been referred to by commercial interests as "bioaugmentation". Their biodegradative potential was evaluated using laboratory mesocosms (simulations) containing a predetermined optimal waste loading rate based on % oil and grease, mixed with predetermined optimal loading rates of clay and river silt materials. The waste consisted primarily of aliphatic and aromatic hydrocarbons found in buried sludges and abandoned lagoons. All mesocosms received nutrient amendment without additional energy sources. Experimental mesocosms were inoculated with adapted indigenous microflora and/or commercial strains. Microbial ATP, microbial diversity, and related enzyme assays were used to establish the detoxification efficiency of the experimental microflora. Quantitative toxicant concentrations and transformations were documented by GC/MS data. Information will be presented mainly on the kinetics of toxicant biotransformation processes to identify "bioaugmentation" contribution and relevancy in the recovery of abandoned polluted sites.