There are very few automatic procedures in the literature to calculate three-phase envelopes (VLLE boundaries). The best existing procedures require selecting each step manually to complete the three-phase envelope. In this article, a density marching procedure and a saturation point calculation at specified density of one of the incipient phases developed recently for drawing two-phase envelopes is extended to three-phase envelopes. Procedures have been presented to determine three-phase bubble and dew points reliably. Two examples are presented to demonstrate the method. The method has direct application in process simulation and thermodynamic property programs.