Drop calorimetry has been used to measure the heat changes occurring upon the dissolution of some single n-alkanes (octadecane to tetracosane) or their binary mixtures (C22H46-C24H50 and C23H48-C24H50), in ethylbenzene, at 311.45 K. The enthalpy changes measured show the even-odd alternation effect known for n-alkanes. The binary mixtures show pronounced non-ideality. Their enthalpies of formation at 293.15 K were deduced from the measurement of their heats of dissolution in ethylbenzene and found to depend on the crystal type. It is shown that these mixtures may consist of several phases of solid solutions.