We also performed a degree of rate control (DRC) analysis to confirm our prediction of rate-limiting step by evaluating the sensitivity of each elementary step to the overall turnover frequency. The DRC analysis has been performed on all steps in an ethylene oligomerization cycle, leading to the conclusion that the ethylene migratory insertion step, having a DRC for 1-butene formation of 0.95, is the rate-determining step. The turnover frequency is much less sensitive to the β-hydride transfer step, whose DRC values are in the order of 10 -2 . In the results of the dilute feed, the most abundant surface intermediates (MASI) are physisorbed ethylene and Ga-n-butyl species (coverages: 0.54 and 0.46, respectively). The results are consistent with the free energy analysis, where the two species represent reasonable free energy wells. The physisorption step has a negative free energy, and given a relatively high barrier of ethylene insertion, ethylene would accumulate before the elementary step occurs, leading to its higher coverage. Consistent results are obtained using the pure feed, where the physisorbed ethylene on the Ga-ethyl species has an even higher coverage (coverage: 0.99), and the ethylene insertion step remains the rate determining step (DRC: 0.94). Using a simplified rate expression by assuming ethylene insertion being ratedetermining, an Arrhenius plot from microkinetic modeling is included in the Supporting Information (Fig. ), where the apparent activation energy from the free energy analysis is reproduced. This further confirms that the other elementary steps can be treated as quasiequilibration.