We present and discuss the influence of the molecular architecture on the phase equilibria behavior of ethylene glycol oligomers and their mixtures based on predictions from a molecular-based equation of state (EoS). The soft statistical associating fluid theory (SAFT) EoS is used to fit the molecular parameters from the available vapor liquid experimental data, providing a correlation of the molecular parameters with the molecular weight of the compounds, which can be used to predict the behavior of heavy members of the series. The same equation is used to describe the ethylene glycol oligomer mixtures with several compounds, including carbon dioxide, benzene, methane, and n-hexane. The performance of the soft-SAFT equation is compared with some Gibbs excess free energy models and the Peng-Robinson EoS, where soft-SAFT is superior in most of the cases. Once the performance of the equation and the molecular model are established, soft-SAFT is used as a predictive tool to systematically study the influence of the chain length, polarity, and hydrogen bonding formation on the behavior of two selected mixtures. The influence of the oligomers ' chain length is noticeable in the dew points of liquidlike solutes (benzene), with almost no effect in the boiling point of these mixtures, except for the ethylene glycol mixture. On the contrary, the solubility of carbon dioxide on these oligomers strongly depends on chain length, increasing as the alkyl part of the chain increases. This is attributed to the breaking of hydrogen bonds in the shorter oligomers.