A computer modelling algorithm has been developed to represent ternary and quarternary phase diagrams using a combination of custom Mathematica and CorelDRAW! programs in a combination with the commercial phase behavior and properties package CMGPROP developed by the computer Modelling Group (CMG). The three-dimensional phase diagrams (at fixed temperature and pressure) are displayed in true perspective and can be rotated continuously or "folded-out" to facilitate easy viewing of all faces of the diagrams. Sections of these phase diagrams at constant composition of one of the four components can be viewed using a sectioning algorithm which allows one to view two dimensional slices (standard ternary diagrams) of individual phase diagrams or to view the impact of temperature or pressure variations on the placement of various multiphase regions. The quarternary phase diagram construction and sectioning routines were applied to three systems at various temperatures and pressures: a simple ternary hydrocarbon system (methane + propane + n-decane), a model condensate rich reservoir fluid (ethane + n-butane + propane + phenanthrene), and a heavy oil mixture (athabasca bitumen vacuum bottoms (ABVB) + hydrogen). These routines were found to represent the experimental phase behaviour of each system accurately and to provide an efficient visual tool for generating and presenting quarternary and ternary phase diagrams. A combination of the routines is envisaged as a prototype for a phase diagram teaching aid and from a research point of view, the automated construction of phase diagrams allows for easy interpolation of experimental data especially in the case of heavy oil systems where the cost of experiments is high.