A number of microorganisms exhibit the unusual property of being tolerant to high concentrations of organic solvents such as toluene, xylenes, ethylbenzene, 1-octanol, 1-decanol, etc. in the culture medium. These microbes are of utmost importance in industrial processes associated with biotransformations in double-phase systems and bioremediation. In this study we describe some of the tools that can be used to understand the physiological basis underlying solvent tolerance; information that can, in turn, be used to expand the range of industrial microorganisms that exhibit these properties.