Polymerization of ethylene in a CSTR using a combined metallocene catalyst system (combination of an open-face catalyst, such as Constrained Geometry Catalyst, and a conventional metallocene catalyst) was studied. Using the model developed by Soares and Hamielec, and expanded by Beigzadeh et al., a steady-state simulator was prepared. The effects of different process parameters (such as reactor residence time) and kinetic parameters of the combined catalyst system on steady-state values of molecular weight, polydispersity index, long-chain branching frequency, and copolymer composition (in the case of copolymerization with alpha-olefins) were investigated. it was shown how recipes for synthesizing polyolefins with tailor-made MWD, CCD, and LCB frequencies can be designed.