The thermal decomposition of aqueous urea solution was studied in a lab-scale experimental system. The experimental research was focused on the effect of oxygen concentration and different additives on NH3 yields, N2O production, and CO concentration. Without oxygen or additives, the NH3 yields increased gradually as the temperature increased from 473 K to 923 K and remained approximately 60% in the temperature range of 923-1073 K. Oxygen promoted the thermal decomposition process and enhanced the NH3 yields in the temperature range of 473-773 K, but it brought about the oxidation of NH3 and led to significant decline of the NH3 yields when the reaction temperature was above 823 K. The addition of Na2CO3 promoted the NH3 yields obviously, but it did not restrain the NH3 oxidation at high temperatures. Furthermore, Na2CO3 reduced the production of N2O and CO at 623-1073 K. Similar to Na2CO3, the addition of NaNO3 also increased the NH3 yields and decreased the N2O and CO concentration. (C) 2016 Elsevier Ltd. All rights reserved.