The gamma (A 2 S / -X 2 P r ) system of the nitric oxide isotopomers 14 N 16 O, 15 N 16 O, 14 N 18 O, and 15 N 18 O, excited in the anode glow of a two-column hollow-cathode discharge tube, was recorded in the spectral region 2140-2730 A ˚under medium resolution. The gamma system of 15 N 18 O and several bands of 14 N 18 O of this system in emission are reported here for the first time. The rotational structure of the 0-1, 0-2, and 0-3 bands of 15 N 18 O of this system was also recorded under high resolution. The wavenumber data of these three electronic bands and those of the infrared vibrationrotation absorption bands 1-0, 2-0, and 3-0 of the X 2 P r state of 15 N 18 O available from the literature were together used in a global fit, using an effective Hamiltonian method for the 2 P state, and molecular constants were derived for the A and X states. These include the following (in units of cm 01 ) for state A of 15 N 18 O: T 0 Å 44 130.244(2), B 0 Å 1.812980(7), and D 0 Å 4.694(6) 1 10 06 . The present work suggests that the X 2 P r state changes from Hund's case (a) at lower J to case (b) at higher J. From the measured bandhead data the vibrational constants of the X and A states of 14 N 16 O, 15 N 16 O, and 14 N 18 O were also determined.