Abstract: An optimized thermal/catalytic combuster for the efficient oxidation of volatile organic compounds (VOC) in air. As an example, the invention is directly applicable to remedial action for clean-up of ground sites contaminated by spills or leaks of gasoline, organic paint solvents and the like, by a process known as air extraction. A thermal combuster and a catalytic oxidizer are interconnected by piping and control valves so that when one such element operates, the other is quiescent, depending on the concentration of combustible vapors in the extracted air. A dilution air valve, a heat exchanger, an electric heater, or a connection to a supplemental supply of clean-burning fuel, or all these devices, may be provided to ensure efficient operation. In an alternative embodiment, an internal combustion engine may be used in place of the thermal combuster. The engine can be used to supply power for other uses within the system or for external use.