A group of three different perfluoropolyethers (PFPE) has been studied in dilute solution using static and dynamic light scattering, and size exclusion chromatography with a viscometric detector (SEC/eta). The polymers studied were perfluoropoly(ethylene oxide) (PF-PEO), perfluoropoly(trimethylene oxide) (PF-3MO), and a copolymer of perfluoropoly(ethylene oxide) and perfluoropoly(methylene oxide) (PF-PEO/MO). The polymers were separated into narrow molecular weight distribution fractions by supercritical fluid extraction. Molecular weights of the fractions obtained spanned a range from 1500 to 50 000. Molecular weights of several of the fractions and whole polymers were determined by low-angle light scattering and used as calibration standards for the SEC. The intrinsic viscosities in dilute solutions-of 1,1,2-trichlorotrifluoroethane were determined using SEC/eta. Excluded volume interactions are negligible due to the very low molecular weights and the poor thermodynamic quality of the solvent. Deviations from Gaussian chain statistics at these very low molecular weights were observed and the viscometric data were evaluated to obtain unperturbed dimensions using a graphical procedure based on the wormlike cylinder model. Characteristic ratios estimated from the slopes of these plots are 4.9, 5.1, and 5.6 for PF-PEO, PF-P3MO, and PF-PEO/MO, respectively.