Some of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) tri-block copolymers aggregate in pxylene upon addition of ethylene and form reverse micelles at higher temperature at which the reverse micelles cannot be formed without addition of compressed ethylene. An abrupt increase of water solubilization is observed at a certain ethylene pressure. The effects of surfactant structure, such as the ratio of EO (EO weight percent) and the molecular mass, on the copolymer micellization and the solubilization of water in such systems are studied. For the copolymers with the same length of PO block, higher EO ratios facilitate the reverse micelle formation. However, as the EO ratio reaches 70%, it cannot form reverse micelles because the hydrophilicity is too high. For the copolymers with same composition, higher molecular weight is favorable to forming the reverse micelle due to the hydrophilic and folding effects, respectively. The reverse micelle solution can solubilize water with W-0 (molar ratio of water to EO segment) up to 4.1. © 2005 Elsevier Ltd. All rights reserved.