The partial-pressure dependence of the reaction of CO;! with residual organic carbon in retorted Colorado oil shale has been investigated. The reaction was found to depend on the 0.2 power of Pcos for pressures between 20 and 100 kPa (~0.2 to 1 .O atm). Because of this small Pcoz dependence, the simplification of Langmuir-Hinshelwood kinetics proposed by Ergun should well represent the inhibition effects of CO. This result is also compared to other work on pure carbons and coal chars. The effect of various pretreatments on the reactivity of the residual carbon has been investigated. Removal of mineral matter (primarily carbonates) by leaching with hydrochloric acid reduces the reactivity of the residual carbon by more than an order of magnitude. Surface area measurements indicate that the specific surface area of the residual carbon is reduced only slightly upon acid leaching. This implies that the carbon gasification is catalysed by mineral matter in the oil shale. A decrease in the reactivity of the residual carbon is also observed upon thermal treatment. It has been shown that the major cause for the decrease is the deactivation of mineral catalytic species.