Long-lived oscillations in the chlorite ion-iodide ion-malonic acid system and in its derivatives, ClO2-I-2-malonic acid and ClO2-Cl--iodomalonic acid systems, are shown to proceed according to a general type chlorite-controlled mechanism. The slow reduction of ClO2 serves as a continuous source of ClO2-. The moderately fast equilibrium between iodomalonic acid and a reactive intermediate (R) maintains a steady concentration of R at around 10(-6) M during a significant part of the oscillatory cycle. Autocatalytic oxidation of R with ClO2- takes place according to the general model of chlorite-based oscillators. The key to the oscillation is that, at a critical value of [ClO2-],the autocatalytic oxidation becomes faster than the equilibrium and both R and ClO2- are used up, Model calculations as well as experiments in a semibatch reactor have verified this explanation. A dual effect (inhibition-induction) of Cl- on oscillations suggests that ICI or I-2 can be the crucial intermediate.