Here we present an analysis of a binary heterogeneous reaction in a chemostat for the particular case of reagents with unequal mass transfer coefficients. For fast irreversible kinetics, there are two potential steady states-the dispersed phase is preferentially populated by one reagent and essentially depleted of the other. The selection of which steady state occurs depends on the operating parameter which is the concentration ratio sigma of the slower (B) to the faster (A) transferring reagent in the feed stream. The demarcation between these operating regimes is the critical value of this ratio: sigma(crit) = K-A + KAKB/K-B + KAKB, where K-i is the mass transfer coefficient of reagent i. Although the concentrations of each species in each phase are piecewise linear in a, the fact of the crossover of operating regimes can be exploited for the inverse problem of kinetic parameter estimation by introducing an oscillation in the feed concentration with a protocol for frequency and amplitude response. The mass transfer coefficients can be estimated by operating conditions sigma on either side of sigma(crit), permitting the estimate of sigma(crit), which is shown to have the greatest sensitivity to the intrinsic chemical kinetics, even when fast and nearly irreversible. Assimilating data from a single experiment conducted at a sigma = sigma(crit), reliable estimates are made even with classically undersampled estimates of the Fourier coefficients for the fundamental and first harmonic frequencies according to the Nyquist-Shannon sampling theorem. (c) 2005 Elsevier Ltd. All fights reserved.