Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for the ternary mixtures (cyclohexane + benzene + cyclohexanone) and (cyclohexane + toluene + cyclohexanone), and also for the binary mixtures (cyclohexane + cyclohexanone) and (benzene + cyclohexanone). Smooth representations of the data are presented, and are used to calculate constant excess enthalpy contours for the ternary systems.