The complex Al3+/CO was investigated with respect to the equilibrium geometry using ab initio SCF calculations. Two minima have been found, both with linear configurations. The minimum corresponding to CO ... Al3+ is slightly deeper (ΔEO = -0.206062 au) and reveals an elongation of the equilibrium bond length CO (0.1195 nm) with respect to that of isolated CO (0.1102 nm) and a shorter equilibrium distance RO = 0.1743 nm between Al3+ and O. The other minimum corresponding to Al3+...CO amounts -0.198951 au and reveals a shortening of the equilibrium bond length CO (0.1075 nm) and an equilibrium distance RC = 0.2062 nm between Al3+ and C. Using the equilibrium distances from these calculations the 13C, 17O and 27Al NMR chemical shielding tensors were investigated using coupled Hartree-Fock calculations with large gaussian basis sets. The results are compared with 13C NMR investigations of carbon monoxide adsorbed on decationated zeolites.