The triblock copolymer (EO)(27)(PO)(6I),(EO)(27) aggregates in p-xylene upon addition of ethylene, An abrupt increase of water solubilization is observed at a certain ethylene pressure. The molar ratio of water to EO segment (W-0) can be as high as 4.2 under suitable conditions. The reverse micelles can solubilize ionic substances, such as methyl orange. The polarity of the water domains increases with increasing W-0 as shown by a solvatochromic study. The structure of the reverse micelles is characterized by small-angle X-ray scattering and Fourier transform infrared. The results indicate the existence of lamellar structure and "bulk" (hydrogen-bonded) water (H2O and D2O) in the reverse micellar system. The formation and breaking of the reverse micelles can be repeated by adjusting the ethylene pressure.