Hydrogenations of individual C-5 dienic substrates (1,3-cyclopentadiene, isoprene, 1,4-pentadiene, cis-1,3-pentadiene, trans-1,3-pentadiene) and their binary mixtures on a heterogeneous palladium catalyst were studied in cyclohexane at 25 degrees C and 2 MPa. Selectivities of the competitive hydrogenations were determined and the substrates relative adsorption coefficients calculated. Effects of the diene structure on their reactivity and the stability of the surface complex are discussed. It was found that differences in selectivity of the competitive hydrogenations of C-5 dienes are caused by the difference both in adsorptivity values and in reactivity of adsorbed molecules. The presence of a five-membered ring in the C-5 dienes leads to significant reduction of surface complex stability as compared with acyclic structures of C-5 dienes. On the other hand, it has a very positive effect on the rate of surface reaction.