Abstract: The derivation of an expression for the minimal work of micellization (aggregation work) on the basis of the extended droplet model has been considered for the cases of direct and inverse spherical micelles. The contributions of the following factors to the aggregation work have been taken into account: the hydrophobic effect upon the formation of the core of a direct micelle; the electrostatic interaction upon the formation of the core of an inverse micelle; the influence of the conformations of hydrocarbon tails and polar head groups in the corona and core of the direct and inverse micelle, respectively; and the effect of the surface tension at the boundary between a micelle core and a solution. The equation of state of molecular groups on a micelle core surface has been shown to play an important role in describing the stabilization of both direct and inverse micelles. The account of the contributions to the aggregation work makes it possible to explain the mechanism of surfactant aggregation in a nonpolar solvent in the absence of water and ascertain the existence of a critical micelle concentration, as well as to determine the average aggregation numbers of dry inverse micelles at different total surfactant concentrations.