We present evidence for the hypothesis of local equilibrium for a liquid-vapor interface in a one-component fluid, using molecular dynamics simulations. Lennard-Jones/spline particles are studied in a two-phase system that is out of global equilibrium. Equilibrium simulations are first used to establish the equation of state for the vapor and interface. A procedure is developed to define the boundaries of the interface. Finally it is shown that the equation of state for the interface applies also when there is heat and mass transport through the interface. The temperature gradient in the vapor was 10(8) K/m in these studies.