An analysis of experimental data for ternary copolymerizations has been performed by an optimizing calculation method, resulting in the estimation of therijcopolymerization constants. The azeotrope calculation results have been compared to those based on therijconstants found for binary copolymerization. For each set ofrijconstants, the possibility of the ternary azeotropy was studied. The formation of quasihomogeneous ternary copolymers was studied subsequent to the determination of the ternary pseudoazeotropy domains occurring at the intersection of the partial pseudoazeotropy domains.