Measurements of enthalpy increments from the temperature of the ordered phases of low temperatures at 293.4 K up to the liquid phase above the melting point were carried out by differential scanning calorimetry using discontinuous mode temperature programming on 18 multiparaffinic mixtures, prepared by melting pure alkanes, and 4 commercial petroleum waxes. Temperatures and enthalpies of the solid/solid transitions and melting were determined, as well as the total enthalpy variations from the order/disorder transition onset temperature up to the melting end temperature and the heat capacity variations in the ordered solid solution and the liquid phase, as a function of temperature. The comparison of the experimental results with the values, calculated for equivalent ideal mixtures from the thermodynamic data of pure n-alkanes, allows us to highlight a deviation in relation to the ideality in the solid state for all of these mixtures: the ordered solid phase reveals a significant gap in relation to ideality, whereas the liquid mixtures show athermal behavior. The composition characteristic parameters of the mixtures (shape of the n-alkane mole fraction distribution, number of n-alkanes, and percentage of the other nonlinear hydrocarbons in the petroleum mixtures) are closely related to the degree of internal disorder in the solid solutions and thus to the deviation in relation to the ideality in the solid state.