Kinetic models in the system Al–N–O–C–H are useful to predict the time- and temperature-dependent influences of oxygen related species on aluminum nitride (AlN) bulk crystal growth by the sublimation–recondensation (also known as physical vapor transport, PVT) method. The transient oxygen incorporation is modeled based on non-linear regression analyses of experimental mass spectrometric data performed at conditions comparable to those of PVT crystal growth, and can be calculated for any user-specified temperature program. The results are in good qualitative agreement with SIMS measurements taken at several positions along the growth direction of a seeded isometric aluminum nitride crystal. By optimizing growth set-up geometry, source purification process, and growth parameters, the impurity content for the grown crystals decreases significantly to values of 6ppm, 15ppm, and 30ppm for O, Si, and C, respectively, 2.5mm above the AlN seed–crystal interface.