The performance of an isothermal tubular reactor for the two models of a autocatalytic reaction, one considering a cubic autocatalytic reaction (A + 2B --> 3B) and the second considering successive bimolecular reactions (A + B --> X, X + B --> 3B), is analyzed. The two models are shown to have input multiplicity behaviour. Though the conventional steady-state operation gives an identical yield of product B for both the reactions under certain parameters values, the input multiplicity behaviour (yield vs residence time) is different for the two reactions. Further, the effect of feed concentration cycling on the average yield of B is compared under input multiplicity.