Abstarct: The increasing concentration of acidic gases such as carbon dioxide (CO₂) and hydrogen sulfide (H₂S) in industrial streams, particularly in the oil, gas, and petrochemical industries, poses significant environmental and economic challenges. Consequently, the development of efficient and sustainable absorbents for the removal of these gases has attracted considerable attention. In recent years, ionic liquids (ILs) and deep eutectic solvents (DESs) have emerged as novel absorbents due to their advantageous properties, including negligible vapor pressure, high chemical stability, and tunable molecular structures. Given the vast diversity of these compounds and the high cost associated with experimental investigations, the application of accurate computational models such as COSMO-RS for predicting thermodynamic properties—including gas solubility, activity coefficients, vapor pressure, Henry’s law constants, and related parameters—is considered essential. Although numerous thermodynamic models have been developed, most of them require experimental data for property The increasing concentration of acidic gases such as carbon dioxide (CO₂) and hydrogen sulfide (H₂S) in industrial streams, particularly in the oil, gas, and petrochemical industries, poses significant environmental and economic challenges. Consequently, the development of efficient and sustainable absorbents for the removal of these gases has attracted considerable attention. In recent years, ionic liquids (ILs) and deep eutectic solvents (DESs) have emerged as novel absorbents due to their advantageous properties, including negligible vapor pressure, high chemical stability, and tunable molecular structures. Given the vast diversity of these compounds and the high cost associated with experimental investigations, the application of accurate computational models such as COSMO-RS for predicting thermodynamic properties—including gas solubility, activity coefficients, vapor pressure, Henry’s law constants, and related parameters—is considered essential. prediction. In contrast, the COSMO-RS model is capable of predicting thermodynamic properties without reliance on experimental data. In this study, the COSMO-RS model implemented within the AMS software platform was employed to investigate the thermodynamic properties of systems containing eleven ionic liquids and three deep eutectic solvents in contact with acidic gases. Experimental data used for validation were extracted from reliable literature sources. To this end, the COSMO-RS model was first validated. Two reputable studies reported the average relative deviation (ARD) of the model as 69.35% and 30.80%, respectively. In the present work, the same calculations were reproduced, yielding ARD values of 31.23% and 24.70%, respectively, thereby confirming the reliability of the model. Furthermore, in the calculation of thermodynamic properties, the maximum and minimum ARD values were found to be 26.2% and 5.61%, respectively, while the overall ARD across all data sets was 13.71%. These results demonstrate the strong predictive capability of the COSMO-RS model for the thermodynamic properties of the studied systems and indicate that this model can serve as an accurate and efficient tool for the design and screening of advanced solvents for acidic gas removal. In addition, the effects of cation and anion structures in ionic liquids on gas absorption behavior were analytically examined. For most ionic liquids, the anion was found to have a more pronounced influence on carbon dioxide absorption. However, in the case of hydrogen sulfide absorption, both the cation and the anion were shown to play significant roles.