Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for the ternary mixtures x1C5H12O + x2C6H14 + x3CvH2v+2, with v = 10 and 12. Smooth representations of the results are described and used to construct contours of constant enthalpy on a Roozeboom diagram. An analysis of the results in terms of the Flory theory of mixtures is also presented.