Ab initio calculations have been carried out for the three polymorphs of SiAl2O5 in order to study the 170 NMR characteristics of tricoordinated O atoms, C[3], and tetracoordinated O atoms, C[4], that are possibly present in the structure of aluminosilicate glasses. We present delta(iso), C-Q, and eta calculations using the density functional theory-based GIPAW method for all silicon, aluminum, and oxygen sites and in particular for the 14 O[3] atoms, which are bonded to three Al or Si atoms in the andalusite, sillimanite, and kyanite polymorphs of SiAl2O5. The C[4] parameters calculated in kyanite are also compared with the corresponding site in alpha-Al2O3. The calculated values for the Si-29 and Al-27 isotropic chemical shift values as well as Al-27 quadrupolar coupling constants (C-Q) and asymmetry parameters (eta) are in good agreement with experimental data. Apart from in alumina and in grossite CaAl4O7, O-17 NMR parameters have not been measured experimentally yet but the CQ and eta values obtained for all sites are consistent with those previously calculated, and the corresponding chemical shift values are reported for the first time. These calculations suggest that it will be difficult to distinguish O(SiAl2) tricoordinated oxygen atoms from 0[2] ones in aluminosilicate glasses on the basis of O-17 NMR data alone since positions of the signals overlap either in a two-dimensional (delta, C-Q) space or in a 3Q-MAS spectrum. It should be noticed that the tricoordinated O atoms calculated are not surrounded by any cations such as Ca2+ or Nal while O-17 chemical shift values for SiOAl and SiOSi show considerable variations with cation type. Nonetheless, the steric hindrance around highly coordinated oxygen sites is important, and we can assume that the first neighbors of the O atoms are usually only Si and Al atoms. Only OAl4 sites with hexacoordinated aluminum, exhibiting a smaller C-Q and relatively high isotropic chemical shift values, can be clearly distinguished from O[2] sites in a 3Q-MAS spectrum.