Second and third osmotic virial coefficients (A(22) and A(222)) of poly(ethylene glycol) (PEG) in aqueous solution were determined from a simultaneous evaluation of laser-light scattering data (diluted solutions) and isopiestic data (concentrated solutions). In contradiction to literature data, it is found that neither A(22) nor A(222) depends on the molecular mass of PEG. The reasons for the lacking accuracy of previously reported data are discussed. With virial coefficients independent of molecular mass, the osmotic virial equation describes well the available reliable experimental data, which cover PEG 200 to PEG 40000 at temperatures between 278 and 333 K, up to polymer concentrations of about 0.6 g cm(-3) An extrapolation indicates that at about 376 K, both A(22) and A(222) are zero.