Abstract Isobaric vapour–liquid equilibria were measured for the binary systems {n-heptane + (o-xylene, m-xylene, p-xylene or ethylbenzene)} at 101.3 kPa using a dynamic method with circulation in both phases. In thermodynamic calculations using the data, the vapour phase was considered to be non-ideal, and activity coefficients of the components in the mixtures indicate positive deviations from Raoult’s law. After reduction of the data and verification of thermodynamic consistency, various group-contribution models were applied to estimate the isobaric VLE data.