Biological treatment of PAH has been demonstrated to be a feasible and common remediation technology which has been successfully applied to the cleanup of contaminated soils provided that the permeability of the soil is high enough to water and oxygen. Clay-containing soils as well as poor solubility and low bioavailability of contaminants such as PAH limit the biodegradation of these substances. Because bioavailability of the contaminants is of great importance for successful bioremediation, modern soil remediation strategies include physical-mechanical steps, the use of surfactants or other solvating agents, chemical or enzymatic oxidation, and the use of thermophilic bacteria.