The effects of oxygen pressure, temperature, catalyst loading, and particle size of the catalyst support on the cooxidation reaction of mixed thiols were studied systematically in gas-liquid-solid systems. The results have shown that the pore diffusional resistance is the main factor limiting the reaction and the overall cooxidation reaction kinetics is zero order in oxygen and first order in mercaptan. The diffusion-controlled rate law can be represented as r = k(obs)C(RSH). A discussion is presented for the industrial sweetening operation based on the research.