Non-bridged zirconocene complexes activated with methylalumoxane can polymerize monoalkenes to high polymers with very high activity. The main control of molecular weight in these systems is due to beta-H transfer from the growing chain, the effect becoming very remarkable in the case of substituted ethylene monomers and with increasing temperature. This work is mainly devoted to test the real capacity of the subject catalyst to produce structurally controlled oligomers from ethylene or ethylene/alpha-olefin mixtures in good yield by investigating the influence of different reaction parameters. On the basis of the relevant results obtained, conditions were identified favouring the cooligomerization of ethylene with propylene and higher alpha-olefins versus the formation of high molecular weight macromolecules. The role of reaction conditions (catalyst, cocatalysts, temperature, pressure, structure of comonomer and presence of hydrogen) on products structure and yield is discussed with reference to previously proposed chain propagation and chain transfer mechanisms.