The theological properties of association between a hydrophobically modified derivative of poly(sodium acrylate) and a series of nonionic surfactants of oligoethylene glycol alkyl ether type have been studied. The theological properties of these systems are strongly dependent on the nature of the surfactant aggregate. A sharp increase in viscosity and gelation is observed for some systems when increasing the temperature. The temperature of this thermal gelation can be correlated with the transition from micelles to bilayers observed in the binary water/surfactant system. By using mixtures of nonionic surfactants and varing the mixing ratio, it is possible to adjust the thermal gelation temperature over a wide temperature range. The mechanism of thermal gelation is discussed.