Adsorption isotherms for the single-component and multicomponent adsorption of o-nitrophenol hydrogenation reaction species (viz, o-nitrophenol, o-aminophenol, and water) from their methanol solution on Pd-carbon (4.6 wt % Pd) catalyst have been measured at the temperatures (278-308 K) at which the hydrogenation reaction is carried out. Both the single and binary adsorption data could be fitted well to Langmuir type adsorption equations. However, the Freundlich-Langmuir equation gives a better fit to the binary adsorption data. The adsorption of reaction species occurs in the order o-nitrophenol > o-aminophenol >> water and it is strongly influenced by the solvent used.