This study presents mathematical modelling of the properties of vapour-liquid phase interfaces for multi-component mixtures. The developed model can be applied both on a standard case of a planar phase interface and on a spherical interface representing droplets or bubbles. The PCP-SAFT equation of state is utilized for thermodynamic property evaluation. The fundamentals of the presented model lie in the Density Gradient Theory (DGT) used to formulate the governing differential equations. An innovative approach to the problem formulation divides the solution into two parts, an algebraic solution and a differential equations solution, that can be solved individually. The developed solution method can be applied on both interface geometries, for which the density profile is solved as the main quantity describing the interface. In addition to the density profile, the surface tension and adsorptions of mixture components within the interface are computed. Mixtures with CO2 were selected as the demonstrative systems in this work. Modelled mixtures of n-butane +CO2, n-decane +CO2, and SF6 + CO2 were compared with available experimental data for surface tension and also with the predictions of a more general Density Functional Theory (DFT). Based on these comparisons, the model was found to be in a good agreement with experimental data and comparable to the DFT predictions. (C) 2018 Elsevier B.V. All rights reserved.