The effect of constituent matrix on the degradation of hydrocarbons was characterized and evaluated within the context of cooxidation. Current information concerning the cooxidation process applied to hydrocarbons was evaluated and results were used to define a laboratory approach for studying the effects of constituent matrix on degradation rates of 13 polynuclear aromatic hydrocarbons (PAHs) in soil. Four matrices were studied: (1) single constituents applied and incubated singly; (2) a synthetic mixture of PAHs applied and incubated together; (3) a mixture of oil refinery wastes; (4) and a creosote wood preserving waste. Initial soil concentrations of constituents were similar for each matrix evaluated. One soil was used, a Kidman fine sandy loam (Haplustoll, Utah). Incubation conditions and extraction and analysis methods were similar among the studies. Four and 5-ring PAHs were found to disappear more rapidly from soils amended with complex wastes, while degradation rates for 3-ring compounds in all matrices were similar. These results can be interpreted in the context of cooxidation and suggest a potential tool for bioremediation of PAH contaminated soils and the simultaneous protection of groundwater resources through reduction or mitigation of groundwater contamination due to vadose zone-associated PAHs.