The ¹³C NMR chemical shift was used as a probe for the average partition of rotational conformers around the C-C bond in the O-CH₂-CH₂-O segments of polyethylene oxide). Dividing the conformers into a large group of trans and a smaller group of gauche conformers, we concluded that the trans conformers have a higher (downfield) average chemical shift than the gauche conformers. The shift of the main PEO ¹³C line with changing environment was interpreted as an adaption in the partition between the two groups of conformers. Furthermore, the trans conformers had nonpolar character and were favored at high temperatures, whereas the gauche conformers had polar character. The measurements were compared to the predictions of a model proposed by Karlström, and a semiquantitative agreement was found.