This Demonstration computes the isobaric vapor liquid equilibrium diagram at for an ideal binary mixture composed of benzene and toluene. The user can drag the locator to see the various regions delimited by the bubble and dew curves (i.e., the subcooled liquid region, the saturated liquid and vapor curves, the biphasic region, and the superheated vapor region). If the locator is in the biphasic region, the vapor fraction is calculated using the lever rule and displayed in red.