An alternative to thermal oxidation is catalytic oxidation of VOCs, which runs at much lower temperatures — about 500–900 ºF. A regenerative catalytic oxidizer (RCO) uses the same operating principle as RTO, but consumes substantially less auxiliary fuel. The authors have found that in many situations, RTOs can be retrofitted to RCOs. Energy savings after such a retrofit can quickly justify the costs for the catalysts and installation. This article discusses basic RTO and RCO technology with an emphasis on thermal efficiency and energy balance.