An attempt has been made to provide a simple method for the determination of accessible Pt metal fraction in Pt-Sn/Al2O3 catalyst. The complications in Pt-Sn/Al2O3 system arise mainly due to uncertainties involved in the oxidation states of tin : Sn-0, Sn2+ and Sn4+ in the reduced catalyst. H-2, O-2 chemisorption/titrations originally applied to Pt/Al2O3 were extended to the Pt-Sn/Al2O3 system. Two oxygen titration cycles OT1 and OT2 at room temperature were carried out using a dynamic pulse flow technique. Only part of the total Sn in the catalyst is reduced to Sn-0 (15%), which contributes to oxygen uptake. While OT1 is a linear function of the Sn content in the catalyst, the second oxygen titration OT2 gives the accessible Pt metal fraction only. It has been concluded that oxygen chemisorption/titrations at temperatures higher than ambient under dynamic conditions are not reliable for the determination of metal dispersions.