The solubility of isobutene in water + tertiary butyl alcohol (the systematic name is 2-methyl-2-propanol) mixtures has been investigated as part of a major study of tertiary butyl alcohol synthesis from isobutene hydration using catalytic distillation. The experimental conditions covered much wider ranges of concentrations (0 to 7.9 kmol(.)m(-3)) and temperatures (303 K to 353 K) than those in previous studies in order to provide a useful empirical correlation for the catalytic reactor design purposes. The data revealed that the isobutene solubility increased exponentially with tertiary butyl alcohol concentration and decreased exponentially with temperature. Excellent correlations were obtained for both isobutene solubility and the Henry's law constants for isobutene dissolving in water + tertiary butyl alcohol mixtures as a function of tertiary butyl alcohol concentration and temperature. The parameter consistency and the difference of the empirical equilibrium concentration model and the empirical Henry's law constant model are discussed.