- One recently reported application of microemulsions is as a fire-resistant hydraulic fluid where efficacy and stability depend among other factors upon the water-solubilizing capacity of the microemulsion and on the relative concentration of the surfactant. A model for such a microemulsion system has been studied using cryo-transmission electron microscopy (cryo-TEM), 1H NMR self-diffusion, and small angle X-ray (SAXS) and neutron scattering (SANS). The phase behavior of the system containing a 1:1:2 oil:alcohol:surfactant weight ratio is characterized by a single continuous microemulsion region starting from a solution containing no water and approaching the water corner. Along this dilution line, a structural transition sequence: oil drops → short range, noncontinuous lamellar microstructure → weakly hydrated aggregates is inferred as the water concentration is decreased. The local lamellar microstructure, i.e., stacks of surfactant sheets, oil, and water, randomly oriented in space without the long range correlations that characterize a lamellar liquid crystal is imaged for the first time.