Isothermal solubilities at 323.15 K of benzene, dichloromethane, and 2-butanone in poly(methyl methacrylate), poly(butyl methacrylate), and two different poly(methyl methacrylate)-poly(butyl methacrylate) copolymers are reported. Results were obtained for the concentrated polymer regime with a quartz crystal balance and are represented to within experimental error by a modified Flory-Huggins equation.