705-707Studies on oscillatory behaviour of gallic acid with potassium bromate in presence of methyl ketones as co-substrates and various metal-ions as catalysts in aqueous acid medium are reported here. The investigations establish the order of reactivity of single and mixed organic substrate systems and also explore the relative efficiency of metal ions as catalysts in the reaction systems. The Mn²⁺/Fe²⁺ couple has been examined for co-catalyst effect on both single and mixed organic substrate systems