We have studied of the partitioning behavior of both acrylic (AA) and methacrylic (MAA) acids between water and a variety of styrene, acrylate and methacrylate co- and ter-monomer phases. As in single monomer phase systems, the distribution coefficients for multicomponent systems strongly depend upon the hydrogen bond acceptor characteristics of the organic phase and the pH of the aqueous phase. These measured distribution coefficients for multicomponent monomer systems can be predicted by applying an appropriate "mixing rule" to the distribution and dimerization coefficients obtained from the single monomer systems. Using a log-based mixing rule, we have been able to accurately predict the water/monomer distribution characteristics of both AA and MAA for a wide variety of styrene/(meth)acrylate multimonomer systems for our own data as well as those developed by others. This includes multicomponent monomer experiments at pH levels at which the vinyl acids are partially or fully ionized in the water phase.