An improved analytical solution is presented, based on irreversible thermodynamics, that describes the equilibrium distribution of the components of a non-ideal fluid mixture in an 1D, hydrostatic and isothermal system. In such a system, the vertical compositional profile of the fluid at equilibrium will be determined by the interaction of gravitational and chemical potentials. The new analytical solution estimates this profile from the overall composition of the fluid. It is thus more general than the existing solution which requires a knowledge of the fluid composition at a given depth and assumes that the vertical compositional profile of this fluid is already at equilibrium. The solution is demonstrated by comparison against results obtained from previously published molecular dynamics simulations of segregation in a binary mixture and against numerical simulations of a real hydrocarbon reservoir system.