The kinetics of the selective hydrogenation of pyrolysis gasoline (pygas) over commercial Pd/Al2O3 catalyst particles were investigated using a stirred semi-batch reactor in the absence of transport limitations. The effects of reaction temperature and pressure on the conversion of styrene, cyclopentadiene, cyclopentene and 1-hexene were obtained over ranges of temperature (313-343 K) and total pressure (2-5 MPa). Competitive hydrogenation between monoolefins and diolefins was extensive, and the reaction rates of diolefins were much faster than those of the monoolefins. A Langmuir-Hinshelwood type model was proposed and successfully fitted to the experimental data. The kinetic and adsorption parameters were estimated by using the fourth-order Runge-Kutta method together with the Levenberg-Marquardt algorithm, which minimized the residual sum of squares between the experimental concentrations and the calculated values. The orders of the estimated activation energies and the adsorption parameters were consistent with the order of the reaction rates of monoolefins and diolefins.