Wagner constants are estimated from VLE predictions based solely on the critical and normal boiling points, and acentric factor.  The predictions come from the standard forms of 1) Riedel and 2) Ambrose-Walton, 3) a modified Riedel equation resulting from forcing the value of K to provide zero error at the reduced temperature of 0.7, and 4) a modified Ambrose-Walton equation resulting from using a pseudo acentric factor that provides zero error at the normal boiling point.  Reduced vapor pressure values obtained using these Wagner constants are compared to those generated by using literature-reported Wagner constants that are applicable for the entire two-phase VLE curve for 72 species. It is shown that the Wagner equation parameterized using VLE predictions from such correlations can provide better accuracy than the underlying source correlations themselves, and it can exhibit less error than a parameterization using a limited interval of experimental data.