Using the attainable region approach, feasible compositions and conversions for random copolymers are determined, along with alternatives for the related reactor configurations. This analysis attempts to find all of the possible compositions that can be produced by any system of reactors and mixing. The average copolymer compositions are bounded by the feed composition and the instantaneous copolymer composition produced at the initial conditions. Since the instantaneous copolymer composition can be found through the Mayo-Lewis equation, that case and the feed composition mark the limiting feasible compositions. The results can also be used to determine the range of feed compositions for which a specific copolymer product composition is possible. If the addition of monomer at any point in the reactor system is possible, e.g., by side-feeding, the analysis indicates that any desired copolymer composition can be obtained.