The thermodynamics of hydrogen adsorption on palladium catalyst supported on silica is determined by isosteric analysis of series of isochores measured by the volumetric method. The variations of this thermodynamics (Delta H, Delta S) with adsorbed amount allows the discrimination between the different hydrogen species present on such a catalyst (hydrogen strongly and weakly chemisorbed on the palladium, absorbed in the palladium particles and molecularly adsorbed on the support). Namely, the variations of only the heat of adsorption with adsorbed amount allow the determination of hydride and weakly adsorbed hydrogen species. It is shown that these amounts can even be determined from one single isochore.