© 2018 Elsevier B.V. In this work, we perform measurements of the thermal transport properties of heptane-isooctane mixtures in the liquid phase at room temperature and atmospheric pressure. The thermal conductivity, k, was measured using the transient hot-wire (HW) method, and the thermal effusivity, e, was determined by the front photopyroelectric (FPPE) technique. Then, the thermal diffusivity, α and the heat capacity per unit volume, C, were calculated using the well-known relationships α = (k/e)2 and C = e2/k, respectively. We show that a correlation between these parameters and octane number exists, and that the obtained thermal parameters proved to be sensitive to detect molecular associations in binary hydrocarbon liquid mixtures. We also report about the thermal conductivity of mixtures of n-alkanes vapors and air showing that almost similar values are obtained for heptane and isooctane, so that octane number rating using the well-established binary mixtures of these substances becomes impossible with thermal properties measurements in the gas phase.