Mass removals due to volatilizatio n and biodégradation were quantified during air sparging trials in a sand aquifer contaminated by dissolved petroleum hydrocarbons (mostly BTEX—benzene, toluene, ethylbenzene and xylene). Volatilization was determined from measurements of volatile organic compounds in extracted soil gas and biodégradation was evaluated from oxygen utilization in the aquifer. The removal of the dissol­ ved petroleum hydrocarbons from the aquifer was also determined in relation to the distribution of sparged air and dissolved oxygen in the aquifer. Volatilization was the dominant mechanism and petroleum hydro­ carbons were removed from the air contact zone within 1-2 days. An evaluation of the rates of biodégradatio n was complicated by trapped air in the aquifer and other sinks of oxygen. However, biodégradation rates were at least an order of magnitude less than volatilization rates when most dissolved petroleum hydrocarbons were being removed.