The coexistence vapour-liquid properties of higher rt-alkanes of large anisotropy (pentane, decane, and pentadecane) modelled by rod-like Kihara fluids were determined using Gibbs-ensemble (GE) and extended Gibbs ensemble (EGE) Monte Carlo simulations. We found that for dense, low temperature states the EGE becomes more accurate and efficient than GE. Comparison of the simulation results with those of a second-order perturbation theory shows that, surprisingly, the theory performs reasonably well for models of large elongations (pentadecane) but disagrees considerably for the model of pentane.