Diffusion-ordered NMR spectroscopy (DOSY), a technique based on pulsed field gradient NMR (PFGNMR), was used to characterize molecular weight distributions for samples of poly(ethylene oxide) in D2O. The distribution of diffusion coefficients G(D) was obtained by analysis of PFGNMR data with a modified version of the well-known constrained regularization program CONTIN. Regularization was considerably improved for broad distributions by setting the weights c(m) in CONTIN’s quadrature formula equal to (D-m/D-max)(m)(x) where D-max is the diffusion coefficient corresponding to the maximum in G(D-m)D-m and m is an index. Here x(m) varies linearly from +2 to -2 with log(D-m) across the distribution. This amounts to enhancing low amplitude regions of G(D)D during analysis. The estimated distribution was then converted to the mass weighted distribution of molecular weights by means of the relation D = 10(-7.62) M(-0.62) (With D in units of m(2) s(-1)) obtained from experiments on monodisperse reference standards. In this study spin relaxation rates were independent of molecular weights and intermolecular averaging effects were insignificant. As an illustration, molecular weight distributions were determined for two broadly distributed samples. The number and weight average molecular weights and the polydispersities agreed well with values provided by the manufacturer when the PFGNMR data sets had signal-to-noise ratios greater than 500.