The aim of this paper is to determine the liquidus surface of the pseudoternary system {C14H30 tetradecane/ C14H10 phenanthrene/wax} to display the influence of the phenanthrene C14H10 on the solubility of a petroleum wax in the normal tetradecane C14H30. The binary diagram {C14H30 tetradecane/C14H10 phenanthrene}, the two pseudobinary diagrams {C14H30 tetradecane/wax} and {C14H30 phenanthrene/wax} and three vertical sections, through ternary space diagram from pure tetradecane (C14H30) to three points on the opposite binary {C14H10 phenanthrene/wax}, are established by X-ray diffraction and differential thermal analyses. The polythermal projection of the liquidus surface displays three eutectic valleys in the pseudoternary system. The eutectic valley, whose origin is the binary eutectic of the system (C14H10 phenanthrene/wax) borders the pseudobinary system (C14H30 tetradecane/wax) with lower crystallization temperatures, and therefore, for a mixture, whose wax/C14H30 tetradecane ratio is constant, the addition of phenanthrene decreases the amount of the wax deposited as far as C14H10 phenanthrene concentrations close to the eutectic valley.