This work presents an exhaustive mathematical model for the high pressure polymerization of ethylene in tubular reactors of configuration similar to that encountered in the industry. Multiple injection of monomer, mixtures of initiators and chain transfer agents are considered together with realistic flux configurations. Typical heat transfer coefficients are estimated from industrial plant data, The effects of pressure pulse on the reactor behavior are also analyzed. Instantaneous temperature profiles produced by such pressure pulse were recovered from stationary simulations showing a very good agreement with the corresponding experimental data. The model features are demonstrated by predictions of temperature, concentrations of reactants and products and molecular properties as a function of reactor length. Also, appropriate predictive capabilities are disclosed by comparison of model simulation results and experimental data. The generation of a high temperature initiator, derived from oxygen, is assessed by comparison of temperature profiles corresponding to runs with and without oxygen.