The UNIQUAC model in combination with the Peng–Robinson and the Hayden–O’Connell Virial equation of state was used for correlating vapor–liquid equilibrium for a gas–solvent system containing the following: CO2–water, CO2–ethanol, CO2–acetic acid, CO–water, CO–ethanol, CO–acetic acid, CH4–water, CH4–ethanol, CH4–acetic acid, N2–water, N2–ethanol, N2–acetic acid, H2–water, and H2–ethanol. Prausnitz and Shair correlation, for the fugacity of the hypothetical liquid solute at a pressure of 1 atm, was implemented in the parametrization procedure as additional objective function so as to reduce the uncertainty on the constants of the model. The results show that the UNIQUAC equation, coupled with an appropriate equation of state to model the vapor phase nonideality, is able to represent the binaries in the range of temperatures and pressures considered in the study, i.e., from 0 to 310 °C and from 1 to 400 bar, respectively. In addition to model parameter estimation, a new generic method to evaluate gas solubility in mixed solvents based on the thermodynamic relation of Henry’s law constant with the activity coefficient at infinite dilution, has been derived. Given the binary parameters of a generic excess Gibbs energy model, the gas solubility in the multicomponent system can be readily estimated.