This report applies a Job plot analysis to demonstrate that dialkyl Zn reagents mediate chain transfer between Hf-pyridyl amido polymerization catalysts and AlR₃ chain-transfer agents. Polyoctene produced in the presence of both ZnEt₂ and AlEt₃ is lower in molecular weight and has a narrower distribution than polyoctene produced in the presence of ZnEt₂ alone. I₂ labeling and NMR analysis of polymer chain ends enable quantification of the amount of Zn- and Al-polymeryls produced during polymerization. A Job plot of the number of Zn and Al polymer chains produced versus the mole fraction of ZnEt₂ at constant moles of Zn + Al reveals a nonlinear relationship. The nonlinearity of the Job plot indicates cooperative exchange between Zn and Al. The chain-transfer agent, AlEt₃, inhibits initiation, but not propagation, of polymerization as catalyzed by the Hf-pyridyl amido complex. This inhibition can be obviated by a two-step polymerization protocol. AlⁱBu₃ does not inhibit initiation or propagation and can be used as a chain-transfer agent without the need for a two-step polymerization protocol. Chain transfer using the ZnEt₂/AlⁱBu₃ system is not as efficient as ZnEt₂/AlEt₃, presumably due to the increased steric bulk of the isobutyl groups.