This study revealed a linear correlation between the nanometer-scale oil droplet sizes estimated using small angle X-ray scatterings (SAXS) and the Xe-129 NMR chemical shift in an oil-in-water ternary inicroemulsion system comprising pentaethylene glycol mono-n-dodecyl ether, n-decane, and deuterium oxide. The absolute values of the droplet size estimated using Xe-129 NMR show good agreement with those using SAXS. We also found that the results are consistent with a reported relation derived using small angle neutron scattering. The results suggest the validity of Xe-129 NMR chemical shifts for investigation of colloidal systems to evaluate their internal structures' characteristic sizes. (C) 2007 Elsevier B.V. All rights reserved.