A segment-contribution method for the estimation of Vapor pressure of large, oligomeric molecules encountered in oleochemical industry is described. The method makes use of segment composition, number of segments, and four parameters per segment to estimate vapor pressure as a function of temperature. For major components that occur in crude tall-oil (CTO) distillation, the optimum parameters are reported and the method is shown to be accurate. The open architecture of this segment contribution approach permits the use of new segments, or the treatment of whole molecules as segments if necessary.