We report experimental characterization of O-17 quadrupole coupling (QC) and chemical shift (CS) tensors for the phenolic oxygen in three L-tyrosine (L-Tyr) compounds: L-Tyr, L-Tyr center dot HCl, and Na-2(L-Tyr). This is the first time that these fundamental O-17 NMR tensors are completely determined for phenolic oxygens in different ionization states. We find that, while the O-17 QC tensor changes very little upon phenol ionization, the O-17 CS tensor displays a remarkable sensitivity. In particular, the isotropic O-17 chemical shift increases by approximately 60 ppm upon phenol ionization, which is 6 times larger than the corresponding change in the isotropic C-13 chemical shift for the C-zeta nucleus of the same phenol group. By examining the CS tensor orientation in the molecular frame of reference, we discover a "cross-over" effect between delta(11) and delta(22) components for both O-17 and C-13 CS tensors. We demonstrate that the knowledge of such "cross-over" effects is crucial for understanding the relationship between the observed CS tensor components and chemical bonding. Our results suggest that solid-state O-17 NMR can potentially be used to probe the ionization state of tyrosine side chains in proteins.