The results of differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) on C 6 0 (x) - C 7 0 (1-x) (0<x<1) fullerene alloys are presented. Samples have been prepared by solubilizing weighed amounts of C 6 0 and C 7 0 in toluene and then evaporating the solvent, and by subliming C 6 0 - C 7 0 powders under dynamic vacuum. Dilute alloys prepared from toluene solution undergo the orientational transition at lower temperatures than pure C 6 0 and C 7 0 the depression of the transition temperature depending on the alloy fraction. These samples also exhibit a large miscibility gap for 0.04<x<0.95. In contrast, alloys prepared by sublimation are miscible in all proportions, at least in the high-temperature fee phase. The experimental solubilities are compared with the calculated binary phase diagram, in which intermolecular interactions are treated by the Girifalco potential.