The design for sin apparatus to measure the solubility of gases in polymers is presented. The appmtus is based on a pressure decay method and utilizes a three-chamber configuration for achieving multiple experimental pressures with the same sample. The design was tested using polystyrene (PS) and (CO₂) at temperatures of 100 and 160 °C and pressures up to 12 MPa. The pressure-specific volume-temperature (PVT) data of the PS-CO₂ combination were used to correct the solubility data for the swelling effect of the polyrner. The results indicated that the solubility increascd with increasing pressure and decreased with increasing temperature. However, the data did not compare favorably wiih the literature, since the typicd Henry's law behavior was not observed. The main source of error was believed to be due to the pressure transducer setup in which the msducer, because of its limited temperature range, was placed extemal to the main experimentai setup.