Systems with several components were considered by Yeh and Tripathi [1989], focusing on the choice of primary variables and the coupling of transport equations to chemical reactions. With LEA, they recommended total analytical concentrations of aqueous components as primary variables, pointing out that these would describe any possible state of the system. Under nonequilibrium reactions, appropriate phase concentrations would be primary also. To avoid excessive computational burdens and make inclusion of kinetics feasible, they recommended coupling by sequential iteration. This work on single-phase transport is cited here because multiphase analogues of these suggestions essentially coincide with the practice of state-of-the-art generalized compositional petroleum reservoir simulators [ Young and Stephenson, 1983; Watts, 1986], where primary variables may be total component mole numbers rather than concentrations in order to simplify certain coefficient evaluations.