This paper contains new, representative reference equations for the thermal conductivity of o-xylene, m-xylene, p-xylene, and ethylbenzene. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. In the case of the dilute-gas thermal conductivity, a theoretically based correlation was adopted in order to extend the temperature range of the experimental data. Moreover, in the critical region, the experimentally observed enhancement of the thermal conductivity is well represented by theoretically based equations containing just one adjustable parameter. All four correlations are applicable for the temperature range from the triple point of each fluid to 700 K, and an upper pressure limit determined by the maximum density limit for the equation of state used to provide density. At the upper temperature limit of 700 K, the maximum pressure was 200 MPa for m-xylene and p-xylene, but 60 and 70 MPa for ethylbenzene and o-xylene, respectively. At lower temperatures, the maximum pressure is lower. The overall uncertainty (at the 95% confidence level) of the correlations of the thermal conductivity of o-, m-, p-xylene, and ethylbenzene, over their range of applicability, varies for each fluid. For o-xylene, we estimate the uncertainty for liquid and supercritical densities for temperatures from the triple point to 400 K to be 2.6%, and 4% at higher temperatures, and in the dilute-gas region we estimate the uncertainty to be 2%. For m-xylene, the estimated uncertainty for liquid and supercritical densities at temperatures from the triple point to 375 K is 3.6%, and 5% at higher temperatures, and 6% for the dilute gas. For p-xylene, the estimated uncertainty for liquid and supercritical densities at temperatures from the triple point to 700 K is 3.6%, and 2.5% for the dilute gas. Finally, for ethylbenzene the estimated uncertainty for liquid and supercritical densities at temperatures from the triple point to 400 K is 2.8%, and 2.5% in the dilute-gas region. Uncertainties in the critical region for all four fluids are much larger, since the thermal conductivity approaches infinity at the critical point and is very sensitive to small changes in density.