Several kinds of carbon microbeads and noble metal Powders have been tested as an additive to the iron(II) phthalocyanine-based sensing electrode (SE) for the.amperometric oxygen sensors; AgAg6I4WO4PbSnF4SE, O2. The use of the SE containing surface-modified carbon microbeads enables the sensors not only to respond fast at room temperature but to exhibit the highest sensitivity. Furthermore, it is capable of determining oxygen partial pressures of 2-750 kPa in a wide operating pressure range 10 kPa-3.5 MPa.