Excess molar enthalpies, measured at the temperature 298.15 K and atmospheric pressure conditions by means of a flow microcalorimeter, are reported for the ternary mixtures {x(1) dipropyl ether + x(2) dibutyl ether + (1 - x(1) - x(2)) (1-hexene or tetrahydrofuran)}. A smooth representation of the results is described and used to construct constant-enthalpy contours on a Roozeboom diagram. It is shown that good estimates of the excess molar enthalpies of the ternary systems can be obtained from the Liebermann-Fried model by using the physical properties of the pure components and the parameters determined from their binary mixtures.