The paper deals with the application of the micelle formation theory, developed by Nagarajan and Ruckenstein [R. Nagarajan, E. Ruckenstein, Langmuir 7 (1991) 2934-2969] and Nagarajan [R. Nagarajan, in : K. Esumi (Ed.), Structure-Performance Relationships in Surfactants, Dekker, New York, 1997, pp. 1-81; R. Nagarajan, Adv. Colloid Interface Sci. 26 (1986) 205-264] to various n-alkyl-beta-D-glucopyranoside surfactants, differing in the surfactant tail length (n-octyl-beta-D-glucopyranoside C(8)G(1), n-decyl-beta-D-glucopyranoside C(10)G(1) and dodecyl-beta-D-glucopyranoside C(12)G(1)). The model predicts that the carbohydrate surfactant molecules assemble for energetic reasons in spherical bilayer vesicles. The critical micellar concentration as function of the temperature shows a minimum value. The formed micellar aggregates exhibit a broad distribution of sizes. It is demonstrated in this study that the thermodynamic theory in combination with phase separation thermodynamics can be used successfully to described the phase separation, which occurs for the system C(10)G(1) + water and C(12)G(1) + water at low surfactant concentrations. (C) 1998 Elsevier Science B.V. All rights reserved.