The interaction of ozone with bio-fuel has been investigated. The highly reactive gas promotes accelerated oxidation, along with changes of the electrical conductivity. The materials specific parameter is monitored by a specially designed thin-film resistor sensor, integrated within a micro-fluidic flow cell. Recordings of the ozone induced conductivity (OiC) are presented for bio-diesel samples, processed from cotton seed oil, blended with and without antioxidants, as well as for fuel grade ethanol, and for commercial Petrol-Diesel, serving as a reference. The time delay between onset of ozone induced oxidation and associated increase in the electrical conductivity defines the oxidative stability, usually revealing a time span, ranging from minutes to hours. For comparison, Rancimat tests have been performed for the same samples. Comparable induction times were obtained for the OiC method under low ozone flux conditions. The set-up is an easy to implement proposed test method, and allows for electronic on-line fuel quality monitoring. (C) 2011 Elsevier B.V. All rights reserved.