Aromatic hydrocarbons, particularly benzene, toluene and xylene (BTX), are major contaminants at many hazardous waste sites. We studied volatilization and biodegradation of BTX from unsaturated soil through bioventing. Following inoculation with indigenous soil microorganisms obtained from the Dagang Oil Field in Tianjin, China, varying amounts of BTX were added to soil in a stainless steel column provided with a constant flow of CO2- free air and pure N-2. Volatilization-to-biodegradation ratios of benzene, toluene and p-xylene were 6:1, 2:1 and 2:1 respectively. Final concentrations recorded in soil gas after three weeks were 0.128 mg/L benzene, 0.377 mg/L toluene and 0.143 mg/L p-xylene. Interactions between the contaminants occurred: benzene and p-xylene degradation were accelerated while toluene was being degraded, and the presence of p-xylene increased the lag period for benzene degradation.