The osmotic pressure of aqueous poly(ethylene glycol) (PEG) solutions (400 and 8000 g/mol) was measured by sedimentation equilibrium (SE) ultracentrifugation over a concentration range of 0-50 wt % and over a temperature range of 10-40degreesC. We have developed a procedure to cover a large polymer concentration range by performing a series of ultracentrifugation experiments at different loading concentrations. The SE data agreed well with previous measurements made using a vapor pressure osmometer. To facilitate conversion from concentration to osmotic pressure, the data were fitted to multivariable polynomial expressions as a function of the PEG-to-water ratio G and temperature T. The osmotic pressure of PEG solutions decreases with increasing temperature. We attribute this behavior to the release of structured water associated with the PEG chains which compared to bulk water has a lower entropy.