The effect of addition of ethylene glycol (EG), ethylene glycol monomethyl ether (EGMME), and ethylene glycol dimethyl ether (EGDME) on the solubility behavior of CaSO4 center dot 2H(2)O in aqueous NaCl solutions has been examined at 35 degrees C. Addition of EG/EG derivatives reduced the solubility of CaSO4 center dot 2H(2)O in general. Replacement of the hydroxyl group of EG by the methoxy group decreased the solubility of CaSO4 center dot 2H(2)O in the order: EGDME > EGMME > EG. We also measured precise density (rho) and speed of sound (u) data for the quaternary systems CaSO4 center dot 2H(2)O + NaCl + H2O + EG/EG derivatives at 35 degrees C. Measurements of speed of sound and density have been used to determine the solution isentropic compressibility (kappa(S)). Empirical equations describing the solubility, density, speed of sound, and isentropic compressibility in these systems are presented.