Conformational properties of ethylene glycol, oligo-, and poly(ethylene oxide) ranging in weight-average molecular weight (M-w) from 62 to 1.1 x 10(7) have been studied by static light scattering and viscometry in salt-free and 0.45 M K2SO4 water and in benzene. Above M-w = 6 x 10(3), intrinsic viscosity ([eta]) and z-average square radius of gyration ([S-2](z)) of PEO in a salt-free solution at 25 degrees C, [eta] = 4.33 x 10(-4) M-w(0.679) dl g(-1) and [S-2](z) = 4.08 x 10(-18) M-w(1.16) cm(2), respectively. The second virial coefficient is positive in water at 25 degrees C but one order of magnitude smaller than reported by Devanand et nl. (Macromolecules, 1991, 24, 5943). A theta-temperature for PEO in 0.45 M K2SO4 aqueous solution is determined to be 34.5 degrees C and above M-w = 4 x 10(2), [eta] and ([S-2])(z) follow the power laws for an unperturbed polymer chain. The characteristic ratio (C-infinity) of PEO is 5.2 +/- 0.1. 9.3 Angstrom was determined for the persistence length and 8.7 Angstrom(-1) for the molar mass per unit contour length of a PEO chain, based on the helical wormlike touched-bead model. The PEO chain in water behaves as a flexible polymer with a relatively large hydrodynamic diameter (9 Angstrom) because of the hydration of the PEO chain.