The long-time behavior of a reaction mixture containing infinitely many species in isothermal continuous stirred tank reactors (CSTRs) is analyzed and contrasted with that in a plug-flow reactor (PFR). The reaction kinetics considered are irreversible first-order, irreversible coupled pseudo first-order, and reversible first-order. Asymptotic lumped kinetics for the mixture as a whole ave developed as a function of feed properties and reactor type. Such lumped kinetics in many cases are of the power law form, with the exponent for a CSTR being lower than that for a PFR. Conditions under which non-power-law kinetics arise are given. Due to the wide spread of reactor residence times, the mixture in CSTRS admits a much richer variety of asymptotic possibilities than in the PFR. The results uncover some behavioral differences and relationships between CSTRs; and a PFR for converting complex mixtures such as petroleum distillates or coal liquids.