The behaviour of a system composed of malonic acid (MA), KBrO 3 , H 2 SO 4 , and ferroin was investigated in batch experiments at various concentrations of oxygen above the chemical mixture when changing the concentration of MA. We could observe that at 10% of oxygen or more and for initial concentrations of malonic acid [MA] 0 between 0.15 M and 0.6 M the system attains an equilibrium by some of mixed mode oscillations. Such a behaviour of the system could be described by a model used lately. Additionally for [MA] 0 = 0.1 M or less at 0 -20% of oxygen a region of sequential oscillations was discovered (observed for the first time in the system with ferroin) and a trial of understanding of the event is suggested. For rather small [MA] 0 ca. 0.025 M no mixed mode oscillations, no sequential ones but the so-called relaxation oscillations were observed.