Multicomponent diffusion between liquid and vapor phases is analyzed for a closed system at high pressure. The movement of the interface during the diffusion is taken into account. The principle model used is the Fick's law in one-dimensional form, which is a second-order partial differential equation with respect to time and a spatial dimension. The model is solved using fixed grid explicit finite difference method. The Fick diffusivities are estimated at each iteration using the Maxwell-Stefan approach, which decouples the drag effects from the thermodynamic nonideality effects. It is found that the thermodynamic correction factor, due to nonideality effects, enhances the off-diagonal Fick diffusivities for gases at high pressure, particularly near critical conditions. The off-diagonal diffusivities in turn make a significant change on the composition-time trajectories. (C) 2004 Elsevier Ltd. All rights reserved.