The reverse micelle formation of AOT in n-heptane, n-octane, isooctane, n-decane, and eucalyptol has been microcalorimetrically studied. From the thermograms, the critical micellar concentration (cmc) and the energetic parameters of standard enthalpy and free energy and entropy of micellization (Delta H-m, Delta G(m), and Delta S-m respectively) have been estimated. From the microcalorimetric titration of AOT/oil mixtures with water up to the phase separation point, the enthalpy of water dispersion (Delta H-d) in the amphiphile/oil medium forming a microemulsion has been also determined. The water dissolution process has shown endothermic enthalpy changes in three distinct stages with an initial enthalpy maximum (except for the AOT/eucalyptol system). Delta H-d has been estimated from the solubility limit, and the entropy of dispersion (Delta S-d) has been consequently obtained from the Gibbs equation. The concentration of the dispersed microdroplets required in the above calculations has been estimated by measuring the droplet size by the DLS method and the known composition of the solution.