Isothermal vapor-liquid equilibrium (VLE) data for 1-butanol + 1-butene were measured at (318.4 and 364.5) K with a static total pressure apparatus. In addition, isothermal VLE data for 1-butanol 2-methylpropane, + n-butane and l-butene + 2-methylpropane were measured at 318.4 K with the same apparatus. Measured p-T-z data were reduced to liquid and vapor phase compositions using the Barker method. For the reduced data, the Wilson parameters were regressed. Using the measurements reported in the literature (when available) for the infinite dilution activity coefficients and the excess enthalpy together with the reduced p-T-x-y data in the parameter regression, another set of Wilson parameters was obtained with better predictive capabilities. UNIFAC-Dortmund was tested against the VLE data reported here and also the literature measurements. The approximate 95% confidence limits are given to all regressed parameters presented in this article.