The chemisorption of H 2, O 2 and CO, and the H 2 O 2 titration method were used for determining the accessible metal fraction of coked Pt/Al 2O 3 reforming catalysts. Several Pt/Al 2O 3 catalysts with different metal loading and metal particle size were employed. A high pressure run using naphtha as feed was performed to coke the samples. Gas uptakes were compared with the catalytic activity of benzene hydrogenation. It was found that the irreversible CO adsorption may be taken as a measure of the accessible metal fraction of coked Pt/Al 2O 3 catalysts; both oxygen and hydrogen uptakes led to wrong results. On the other hand, when the metal dispersion will be determined, it is necessary to eliminate the coke on the metal by O 2 treatment at high temperature which can sinter the metal. The appropriate conditions to eliminate coke with no modification of the metal fraction were investigated by CO chemisorption and electron microscopy. The coke burning by air treatment at 703 K was found to be adequate to eliminate the coke on the metal, with no measurable modification on the metal dispersion.