We show using non-equilibrium molecular dynamics that there is local equilibrium in the surface when a two-phase fluid of n-octane is exposed to a large temperature gradient (10(8) K/m). The surface is defined according to Gibbs, and the transport across the surface is described with non-equilibrium thermodynamics. The structure of the surface in the presence of the gradient is the same as if the interface was in equilibrium, as measured by the variation across the surface of the pressure component that is parallel to the surface. The surface is in local equilibrium by this criterion and because the equation of state for the surface was unaltered by a large heat flux. The surface has a small entropy and is thus more structured than a surface of argon particles. The excess thermal resistance coefficient and the coupling coefficient for transport of heat and mass were calculated and found to be smaller than corresponding coefficients from kinetic theory and for argon-like particles, probably because molecular vibrations contribute to heat transfer. Away from the triple point, the heat of transfer was more than 30% of the value of the enthalpy of evaporation, which means that the surface has a large impact on the heat flux across it. This will be of practical importance in non-equilibrium models for phase transitions. The results support the basic assumptions in non-equilibrium thermodynamics and enable us to give linear flux force relations of transport with surface tension dependent transfer coefficients.