Equations are derived for computing the concentration of each reagent entering an epitaxial reactor from a gas train. The two basic types of systems are: (a) a main diluent stream, part of which is diverted through a number of parallel saturators, each containing several mutually miscible components; and (b) an all‐gaseous system with several dilution stages. In addition, the equations for a hybrid system, which combines the two types, are also derived. The equations have no limits on the number of components or dilution stages.