Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for the ternary mixtures (cyclohexane + n-hexane + n-octane) and (cyclohexane + n-hexane + n-dodecane). Smooth representations of the results are described and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. It is shown that reasonable estimates of the excess enthalpies of the ternary mixtures can be obtained from the Flory theory, using only the physical properties of the components and their binary mixtures.