Values of the Onsager heat of transport Q* measured at the n-octane liquid-vapour interface are consistent with the results of molecular dynamics calculations by Simon et al. [J.-M. Simon, S. Kjelstrup, D. Bedeaux, B. Hafskjold, J. Phys. Chem. B 108 ( 2004) 7186.] The measured value of Q* is independent of gas pressure but is affected by variations in the size of the vapour gap over which the temperature gradient is applied. Measurements with added helium indicate that Q* is negative for helium at the surface of n-octane, even though the enthalpy of solution is positive. The helium results can be understood on the basis of an existing model. (c) 2008 Elsevier B.V. All rights reserved.