The modified Claus process is commonly used in oil refining and gas processing to recover sulfur and destroy contaminants formed in upstream processing. In oil refining, in addition to the typical modified Claus plant feed of H2S and CO2, NH3 is also often present. NH3 is a process contaminant and must be destroyed in the front-end furnace of the modified Claus plant, otherwise, it poses a risk of poisoning the catalyst beds and plugging off downstream equipment because of the formation of ammonium salts. In this paper, the pyrolysis and oxidation of NH3 was studied under Claus furnace temperatures and residence times. Experimental data was taken, and new reaction rate expressions were developed for NH3 pyrolysis and oxidation. The derived rate expressions are outlined as follows: the NH3 pyrolysis rate expression r = A exp(-E-a/RT)P-NH3(1.25), where A is 0.00421 mol s(-1) atm(-1.25) cm(-3) and E-a is 16.5 kcal mol(-1), and the NH3 oxidation rate expression r = A exp(-E-a/RT)PNH3PO20.75, where A is 4430 mol s(-1) atm(-1.75) cm(-3) and E-a is 40.0 kcal mol(-1). The rate expression for NH3 pyrolysis matched experimental data within 13% and matched well with published data. The rate expression for NH3 oxidation matched experimental data within 10%.