The solubilities of the quadrupolar molecules benzene and CO in various ionic liquids (ILs) are compared in order to determine the connection between aromatic liquid clathrate formation and CO dissolution in ILs. It was found that both CO Henry's law constants and benzene solubility are remarkably well correlated with each other and with IL molar volume, suggesting both phenomena depend more on the strength of interionic interactions between the ions of an IL rather than the identity of either ion. However, IL ion-quadrupole interactions were found to have an effect for dicyanamide ([N(CN) ] ), where solubility of CO and benzene are affected by destabilizing and stabilizing interactions with [N(CN) ] , respectively. The results suggest both solubility phenomena are related to the incorporation of the solute into an IL host network. Aromatic liquid clathrate formation thus has potential as a facile experimental probe for predicting the relative ability of ILs to physisorb CO .