An acoustic densitometer has been developed for the precision measurement ofPVTdata over a wide range of temperatures and pressures. With this device, changes in the density of a solid or liquid are measured with a precision better than 3 parts in 105. Further, a density change of as much as 15% may be accommodated with no loss in the sensitivity or accuracy of the measurement. Finally, the electronic system used is straightforward, for which components are readily available. The system was tested on the polymer, polyethylene oxide, over a temperature range 10–50 °C and at pressures up to 1 kbar. Volume derivatives were obtained from the data and used to evaluate the Broadhurst‐Mopsik model for linear polymers. The agreement is good for temperatures up to and including 30 °C. In the temperature interval 40–50 °C, changes in the degree of crystallinity of the sample are suggested by the data.