The combustion of carbon monoxide on transition metals is known to exhibit an intriguing oscillatory behavior in reaction rate as well as reaction temperature under certain conditions. Chemical oscillations during the oxidation of CO at atmospheric pressure on supported Pd catalysts were studied bl situ by employing X-ray absorption spectroscopy (XAS) in an energy-dispersive mode. Self-sustained thermokinetic oscillations with a period of about 12 min were found in both reaction temperature and carbon dioxide partial pressure. Energy-dispersive XAS experiments were carried out in situ at the Pd K-edge (24.35 keV) during the occurrence of chemical oscillations with a time resolution of several seconds. An elliptically bent, rectangular Si(400) crystal in transmission geometry was used. From the Pd absorption spectra, a constant phase correlation of edge position (threshold energy) with respect to the observed temperature oscillations could be revealed, This points toward a periodic oxidation/reduction process accompanying the deactivation/activation cycles of the catalyst. Furthermore, an oscillatory behavior in height and position of the first Pd peak was found in the radial distribution function FT(chi(k)). From a comparison with theoretical cluster calculations, it can be deduced that the evaluated oscillations in Pd coordination number and Pd-Pd distance indicate an oscillatory change of the oxygen surface coverage as well as the ratio of linearly and bridged bonded carbon monoxide. Taking these surface-coverage oscillations and the periodic oxidation/reduction process into account, a surface activation/deactivation mechanism for chemical oscillations during CO oxidation on supported Pd catalyst can be confirmed. The activity of the catalyst appears to be decreased by a surface oxidation leading to an increasing concentration of linearly bonded CO molecules. Thereafter, an increasing amount of bridging CO and a decreasing amount of Linearly bonded CO accompany the reduction of the catalyst and subsequently the return to the high activity branch of the reaction.