In rich-exhaust manifold reactors, complete oxidation of carbon monoxide (CO) and hydrocarbons (HC), generally characterized by luminous conditions and high temperatures, is desirable. Some of the conditions necessary for luminous oxidation in an insulated exhaust reactor have been explored with a single-cylinder engine using both leaded and unleaded isooctane. Threshold-reactor air-injection rates required for luminous oxidation in the reactor were determined for engine air-fuel ratios (A/F) between 11.2 and 14.1.Leaded isooctane produced higher unburned HC concentrations in the exhaust than unleaded isooctane when injection air was introduced as well as when no air was added. In addition, oxidation of CO in the reactor was hindered in the tests with leaded isooctane. During one set of experiments, conditions were such that luminous oxidation in the reactor was achieved with the unleaded fuel, but was not achieved with the leaded fuel.In warmup studies, a longer time was required to reach luminous conditions in the reactor when leaded isooctane was used in the engine than when unleaded isooctane was used.