In liquid phase autoxidation Of hydrocarbons, oxygen availability in the liquid phase affects reaction rate and product selectivity. Instead of relying on engineering predictions, this work set out to measure in situ oxygen availability in the liquid phase under oxidation conditions. This was achieved by employing an oxygen sensitive material submersed in the liquid and measuring the change in fluorescence decay with a fluorometet. Mass transfer coefficients (k(L)) of oxygen in benzene and in indan were 3.0 x 10(-6) and 1.3 x 10(-6) +/- 0.1 x 10(-6) m/s, respectively, at 50 degrees C and 19.2 kPa O-2 partial pressure. This enabled the calculation of the maximum oxygen transfer rate and it matched the experimental observations well. Liquid phase oxygen content increased until the oxygen transfer rate and the oxygen consumption rate were balanced, i.e. reached dynamic equilibrium. At high Oxygen consumption rate, the oxygen in the liquid phase was consumed and the oxygen consumption rate matched the maximum oxygen transfer rate. These changes could be monitored in situ over time during oxidation, It was further found that liquid phase oxidation violated key assumptions underlying engineering predictions based on the Hatta number. Notably, the kinetic constant for oxygen consumption changed with time, oxidation did not reach "steady state", and the relationship between oxygen consumption and oxidation rate varied over time.