Lamellar phases of some surfactant water system are not infinite, continuous lamellar planes but several experimental findings showed that they contain water-filled defects with highly curved edges. Here, the polydomain lamellar phase of the pentaethylene glycol dodecyl ether(C 12 E 5 )/decane/water system has been studied by 1 H-NMR pulsed field gradient experiments (PGSE) and 2 H-NMR line shapes of D 2 O, at a constant surfactant (S) to oil (O) weight ratio of 51.8/48.2. Within the lamellar phase of this system, which was observed at S+O weight fraction from 5 to 82 wt%, three types of bilayer organisation have been found. At low surfactant+oil concentrations,