Fractionation of continuously distributed homologous mixtures is described in terms of molecular distributions. The concepts apply to phase equilibrium in vapor–liquid hydrocarbon mixtures and sol–gel polymer mixtures. Models of both differential and finite phase-equilibrium separations are presented when the partition coefficient for the equilibrium distributions is given. Analytical solutions for the distributions, including a similarity solution for a differential fractionation, can be formed. A differential fractionation solution compares satisfactorily with experimental data.