The effect of HTT on the CO2-gasification reactivity of five different coal chars was investigated. The reactivity of three of the five chars was enhanced by HTT up to temperatures of 1673 K to 1800 K. The TSA and ASA of a hvB bituminous coal char decreased considerably by heat treatment. HTT activation was absent for a demineralized char, clearly indicating a correlation between HTT activation and catalysis by inorganics, presumably iron.