The gas-phase hydrogenation of buta-1,3-diene to but-1-ene, trans- and cis but-2-ene, and butane over Pd catalysts was studied. The reaction was investigated in a reactor operating at atmospheric pressure at 0-20 degrees C over a wide range of conversions. Special. attention was focused on the selectivity as a function of conversion. Up to high conversions (low values of buta-1,3-diene mole fractions) selectivity and stereoselectivity toward reaction products were constant. At approximately 85% conversion the selectivity in but-1-ene was seen to decrease. The selectivity and stereoselectivity were described within a framework of the advanced reaction mechanism. Deactivation influenced the activity and selectivity of the reaction. Deactivation kinetics was taken into account, assuming the formation of higher molecular weight oligomerized olefins. The parameters of the kinetic model were estimated with nonlinear regression analysis. Simulations showed that the kinetic model is able to describe selectivity and stereoselectivity behavior in buta-1,3-diene hydrogenation over the whole range of conversions.