The loss of surfactants from systems relevent to micellar flooding, including the influence of oils, alcohols and polymers, was investigated. Our work has demonstrated the critical role of rock mineralogy in determining the type and extent of surfactant loss. The presence of as little as 1% gypsum in samples of kaolinite, silica and alumina caused decylbenzene sulfonate depletion to shift from adsorption-controlled to precipitation-controlled. However, in gypsum-magnesite mixtures, the influence of gypsum was greatly reduced because calcium activity was controlled by carbonate equilibria. The precipitation phenomena has been studied extensively, and a thermodynamic model developed. It has been shown that above the CMC, redissolution of the precipitate occurs due to adsorption of precipitating ions on micelles, which reduces its activity in the bulk. Modifications to surfactant structure were found to greatly enhance salt tolerance. Through addition of ethoxy groups to alkylbenzenesulfonates, salt tolerance can be improved by more than one order of magnitude for Na/sup / and three orders of magnitude for Ca/sup 2 /. Future work will focus on such surfactants as a means to minimize surfactant loss in micellar flooding. 29 figs.