Monofunctional and bifunctional peroxides are extensively utilized in the production of polystyrene. However, their decomposition kinetics is still an important area to investigate. A computer package developed previously by Gao and Penlidis (1996), which was based on mono-functionally initiated polymerization, is extended in this study to cover homopolymerization of styrene using bifunctional initiators. A database of a wide variety of bifunctional peroxides used in polystyrene production is developed along with a database for twelve new monofunctional initiators. The package handles several different scenarios of styrene polymerization, whether it is in bulk / solution or isothermal / non-isothermal medium. The model is tested with a wide range of conversion and average molecular weight data either from the literature or available from industry. Simulation results agree with the data trends, which makes the simulator a very powerful tool in aid of initiator selection and evaluation. At the end of the paper, results on homopolymerizations of acrylates and methacrylates are also discussed.