This work compares the critical lines predicted by six cubic equations of state (EOS) and classical mixing rules with the experimental data available for the mixtures of methane-alkanes up to and including octane. A simple method for calculating the critical line is proposed. The influence of the values of the unlike pair parameter k(12) is followed and analyzed from the point of view of the global phase diagram. It is shown that different cubic EOS can yield similar semi-quantitative and even quantitative predictions with the optimized values of this parameter. The results are compared with the information available in the literature.