Any equation of state capable of representing both the states of the saturated liquid and vapor of a pure substance may in principle be applied to the computation of vapor-liquid pressures (vapor pressures) as a result of the requirement that the fugacities be the same in both phases. This latter requirement is expressed by the simple equality,

In this paper we proceed to develop “generalized” vapor pressure curves in reduced coordinate format (P_{R}^{Sat} as a function of T_{R}) using two cubic equations of state, namely the van der Waals and Redlich-Kwong equations. Secondly, we compare the above results with the predictions of the three-parameter correlation (P_{R}^{Sat} versus T_{R} and w) of Lee and Kesler. All of the above predictions are in turn compared against actual experimental vapor pressure data.