The recent success of analytical quasi-lattice equation of state (EOS) description of r-mer fluids by the present authors leads us to extend the EOS as a group contribution. With a size parameter for each group and an interaction energy parameter between groups, EOS parameters for pure fluids were calculated. Predicted high-pressure phase equilibrium properties of pure alkanes, cycloalkanes, aromatics, carbon dioxide and their mixtures showed good agreements with experimental data. Especially, the present approach predicts phase equilibria of mixtures without employing any type of adjustable binary interaction parameter, As a result, high-pressure phase equilibrium behaviors of both pure fluids and mixtures can readily be predicted solely from information on functional group interactions.