In this paper experimental data on the solid−liquid and solid−solid equilibria in the binary system (docosane + tetracosane) and solid solubility data in the ternary system (heptane + docosane + tetracosane) are presented. For 14 binary mixtures of the two heavy alkanes, DSC measurements were performed to detect the solid−liquid and solid−solid phase transition temperatures. Solid disappearance temperatures were measured for 14 mixtures of docosane and tetracosane dissolved in various quantities of heptane. The experimental results reveal that the solubility curves found in the ternary system correspond to the phase behavior of the binary subsystem studied. At low concentrations of heptane, probably almost ideally mixed crystals are in equilibrium with the liquid phase, while at high heptane concentrations, the solid−liquid equilibrium involves most likely different nonideal solid phases.