Abstract: A method of removing hydrocarbon contaminants from a source stream, which is particularly applicable to removing volatile hydrocarbon contamination (such as from spilled gasoline) from an underground site. The source stream, which may be extracted from an underground site, is typically mixed with an oxygen containing second stream (preferably air) and the resulting mixed stream passed through a catalytic converter. One or more parameters are monitored which provide an indication of oxidation efficiency by the converter, and the flowrate of one (or both) the source and second streams adjusted so as to maintain efficient operation of the catalytic converter as the hydrocarbon concentration of the source stream changes. The monitoring and adjusting can be manual, or automatic.