Liquid thermal conductivities of 29 organic compounds and 15 petroleum fractions have been measured in a transient, relative apparatus of the hot wire type between 20°and 120°C at a pressure of 7.5 atm.Liquid thermal conductivity is a physical property difficult to measure accurately. Natural convection caused by the imposed temperature difference tends to make experimental values too high. It is known now that many data in reference books and handbooks are in error on the high side by 20% or more.Of all organic compounds, toluene has been the one studied most for thermal conductivity.