This paper discusses how detailed studies on flammability at elevated pressures and temperatures can be applied to liquid-phase oxidation of cyclohexane using air/oxygen and lead to an inherently safer process with better productivity. Flammability tests of cyclohexane/oxygen vapor and vapor bubbles under actual oxidation conditions were performed. The flammability of the vapor and vapor bubbles was found to be moderated by the addition of water into the cyclohexane liquid. The added water forms minimum boiling azeotrope with cyclohexane and its vapor renders the cyclohexane vapor and vapor bubble inflammable. Oxidations of the cyclohexane/water azeotrope utilizing pure oxygen were carried out and found to outperform the traditional air oxidation process by a factor of 2. This paper summarizes our work during the past few years toward a safer and better process development for the liquid-phase oxidation of cyclohexane. © 2004 American Institute of Chemical Engineers Process Saf Prog 23: 72–81, 2004