AbstractThe design of absorption processes requires the knowledge of gas solubility data. Because experimental data are often not available, an estimation method must be used. Various methods for the prediction of gas solubilities have been published in the literature. It is shown that none of the described methods provides satisfactory prediction results. Therefore a new method – the modified UNIFAC method – is proposed. This modification of the UNIFAC method takes into account free volume effects. The method has been used successfully for the estimation of carbon dioxide, methane, oxygen and ethylene solubilities in aliphatic hydrocarbons and alcohols at 1