Novel isothermal (P-x-y) vapour-liquid equilibrium data are reported at three temperatures for each of the (1,1,2,3,3,3-hexafluoro-1-propene + 1-butene), (2,2,3-trifluoro-3-(trifluoromethyl) oxirane + 1-butene), and (difluoromethane + 1-butene) binary systems. The experimental values were measured on a "static-analytic" type apparatus which utilized two electromagnetic ROLSI (TM) capillary samplers for repeatable and reliable equilibrium phase sampling and handling. The VLE results are correlated with in-house thermodynamic software based on the "PR-MC-WS-NRTL" model which comprises the Mathias-Copeman alpha function, Wong-Sandler mixing rule, and non-random two-liquid local composition activity model introduced in the Peng-Robinson equation of state. A maximum pressure azeotrope is observed at all temperatures studied for the (2,2,3-trifluoro-3-(trifluoromethyl) oxirane + 1-butene), and (difluoromethane + 1-butene systems), but not for the 1,1,2,3,3,3-hexafluoro-1-propene system. Liquid-liquid immiscibility is not observed for any of the systems studied over the range of temperatures investigated. (C) 2013 Elsevier Ltd. All rights reserved.