The solubilities of isobutene at pressures from 27 to 102 kPa and a temperature of 298.15 K are presented for three mixed solvent solutions: methanol + benzene, methanol + cyclohexane and benzene + cyclohexane. The measured isobutene solubilities are within 5% of being ideal solubilities for methanol + benzene mixtures, within 9% for benzene + cyclohexane mixtures and within 20% for methanol + cyclohexane mixtures, there is a qualitative similarity between the excess volumes and excess solubilities. Henry's constants of isobutene in these solvent solutions are evaluated by two different methods.