The gas-phase reaction between carbonyl oxides and ammonia is investigated by quantum mechanical calculations. The density functional method B3LYP with the basis set 6-311++G(2d,2p) was employed for the geometry and energy optimization of the stationary points along the reaction path. The energies have been refined by CCSD(T) with various basis sets and Gaussian-3 level of theory. The reaction mechanisms are studied for three different carbonyl oxides, H2COO (methyl carbonyl oxide), CH3HCOO (ethyl carbonyl oxide), and (CH3)(2)COO (acetone carbonyl oxide). First, a prereactive complex is formed, where a hydrogen bond is formed between ammonia and the terminal oxygen atom in the COO moiety. Next, a structural rearrangement occurs, leading to the formation of a chemical bond between the nitrogen atom and the carbon in the COO moiety as well as a transfer of the hydrogen atom from nitrogen atom to the terminal oxygen atom in the COO moiety. The newly formed molecule is a hydroperoxide amine. All the studied reactions are exothermic. The estimated reaction rates range from 1.8 x 10(-13) to 6.9 x 10(-14) and to 5.1 x 10(-18) cm(3) molecule(-1) s(-1) for H2COO, CH3HCOO, and (CH3)(2)COO, respectively. This shows that the investigated process are important in locations with intensive farming.