A kinetic study of ethylene homopolymerization and copolymerization is conducted with a supported metallocene catalyst in a gas-phase reactor. An experimental procedure is developed that minimizes the effect of impurities in the reactor and simultaneously yields consistent and reproducible reaction-rate data. The effects of operational parameters such as reaction temperature, pressure, and comonomer concentration on the kinetics of both homopolymerization and copolymerization are investigated. Online perturbation techniques are implemented to determine key kinetic parameters such as the activation energies for ethylene propagation and catalyst deactivation. A reaction-rate order close to 2 is obtained for ethylene homopolymerization from pressure perturbations, while near to first-order dependency is observed in the presence of propylene. To quantify the effects of the operational, parameters, a one-site kinetic model for homopolymerization and a two-site kinetic model for copolymerization are proposed. The necessary kinetic parameters in the model are estimated using the POLYRED(TM) package. The resulting kinetic model represents the kinetic data over a wide range of conditions for this supported metallocene catalyst.