Structural analyses were carried out by X-ray diffraction, at ambient temperature, on mufti-alkane samples whose mole fraction distribution shows a shape of the ' exponential decreasing ' type, as observed in petroleum cuts. Nine samples, whose normal-alkane number varies from 15 to 23, have been studied with mole fraction continuous distributions of normal-alkanes going from C-22-C-36 to C-14-C-36: each mixture differs from the previous sample by the addition of a lighter n-alkane. At the solid state, the mufti-alkane solid samples C-22-C-36 and C-21-C-36 are two-phase, C-20-C-36 to C-15-C-36, three-phase, and the broader distribution C-14-C-36, four-phase. In these polyphase solid systems, whose heaviest n-alkane is always C-36, the average composition of the heavy and middle phases are constant and their structure are isostructural to the beta ' ordered intermediate solid solution, observed in n-alkane binary or ternary molecular alloys; the mean carbon atom number of the light phase decreases as the global average carbon atom number of the synthetic mixtures in relation to the addition of light n-alkanes and its structure simultaneously evolves from the beta ' ordered intermediate solid solution towards the beta '-RI(Fmmm) and the alpha-RII(R3m) disordered solid solutions, observed in pure n-alkanes: the light n-alkane added between each distribution intercalates itself into the structure whose molecule stacking period (thickness) is compatible with its own carbon chain length, in order to reduce the molecular gaps. (c) 2005 Published by Elsevier Ltd.