We have carried out molecular simulations of carbon tetrachloride adsorption on graphite, in order to investigate the role of the octopole in potential models for the CCl/graphite system, and the temperature dependence of the first-order gas-liquid transition in the first adsorbate layer. Two classes of potential model for carbon tetrachloride were considered: the first has 5 LJ sites and the second includes five partial charges to model the leading octopole. Both models are adequate to represent the vapour-liquid equilibrium, suggesting that the octopole makes an insignificant contribution to the properties of the bulk phase. Both models show that adsorbed CCl molecules are delocalized on a graphite surface because of the strong intermolecular interactions. It is found that the LJ sites on the chlorine atoms, not the octopole, play the most important role in matching the experimental isotherm and isosteric heat data with simulation. The heat is constant, across the first-order transition of the first adsorbate layer. The simulation results show that both the magnitude of the density jump, and the isosteric heat across the first-order transition, decrease as the temperature increases. This is in qualitative agreement with the 1972 experimental data of Avgul and Kiselev, but these experimental data exhibit an unusually strong decrease in the isosteric heat, and the coexistence region between the two phases displays an unusual asymmetrical shape. Detailed analysis of our simulation results, together with the calculated isosteric heat from the experimental isotherms of Machin and Ross, show that there may be errors associated with the heat data of Avgul and Kiselev at high temperatures.