With a lower termination barrier than the ethylene insertion step, the 3CN Ga sites favor selective ethylene oligomerization to short oligomers, consistent with the experimental results at 250 °C and 1 atm. Microkinetic modeling results confirm that the ethylene insertion step is rate-limiting. Further, we note that the in the transition state of the facile β-hydride transfer step, an unusual geometry is found for the main group Ga catalyst, where the hydrogen being transferred does not interact with Ga center. This study highlights the capability of a oxide-supported main group metals to perform olefin oligomerization and also provides suggestions to design such catalysts, where the local coordination environment of Ga sites may be tuned to improve the catalyst activity.