In situ EXAFS spectroscopy was used for identifying the surface species involved in the sintering of alumina-supported Pt catalysts under dried oxidizing atmospheres. A Pt/gamma-Al2O3 catalyst (0.62 wt% Pt, 0.88 wt% Cl) was heated in a 2% O-2/N-2 gaseous mixture from 300 to 525 degrees C for about 120 min and then kept at this temperature for up to 720 min. The main observation, which is in good agreement with ex situ TPR experiments, was that chlorine is always present in the surrounding of platinum during the oxidizing treatment, The metal sintering process involved three successive steps during which the chlorine and oxygen coordinations passed through a maximum, whereas platinum coordination exhibited a minimum. Formation of Pt(OH)(4)Cl-2 species was detected at the end of the first step, i.e., when the temperature reached 500 degrees C. After about 4 h of treatment, we deduced that platinum species are made up of a metal platinum core surrounded by a double coating of oxychlorinated species. More precisely, EXAFS experiments suggested that surface platinum oxide is made of rigid PtO6 octahedra, but their assembly led to a largely disordered structure. The absence of a long-range order allows the location of residual chlorine species either between the PtO6 octahedra or at the Pt-oxidized surface shell.