A simplified technique is proposed for the application of cubic equations of state (EOS) to the calculation of vapor pressures of pure compounds and the method can be adapted to any EOS capable of predicting coexisting vapor and liquid phases. The procedure approximates vapor pressures using the zero-pressure liquid fugacity in the low temperature range, allowing a direct estimation of the parameters of a temperature cohesion function alpha(T-r). Estimation of the whole vapor pressure curve, from low temperatures to the critical point, is possible using minimal information about saturation states. The technique proposed here is illustrated for a generalized form of the cubic EOS.