To examine the effects of organic and inorganic amendments on the degradation of petroleum hydrocarbons, we conducted a pilot-scale experiment during the winter and summer periods. Soil samples were analyzed periodically to determine the soil gas amount of volatile organic compound, carbon dioxide flux, consumption of O2 and indigenous bacterial numbers during bioremediation. The initial level of the most contaminated site (10 070 mg hydrocarbon kg-1 soil) was reduced successively to 4 800 mg kg-1 after 4 months and to 1 400 mg kg -1 after 6 months in ex-situ amended soils. The hydrocarbon-degrading microbial populations increased during the treatment as also did soil respiration. Both aerobic and methanogenic conditions appeared to be important at these sites. Methane concentration (500-23 000 ppm) and CO2 production (800-17 000 ppm) varied with the extent of contamination. The bioventing system used in this study aerated a wide area of soil. It was concluded that N and P availability within the organic and inorganic nutrients limited the biodegradation of hydrocarbon contamination. By combination of organic and inorganic amendments a 86% removal efficiency was achieved. Nutrient diffusion varied within the 3 m high decontamination biopile but was sufficient to promote bacterial proliferation in all layers.