We report a systematic solid-state O-17 NMR study of free nucleic acid bases: thymine (T), uracil (U), cytosine (C), and guanine (G). Site-specifically O-17-enriched samples were synthesized: [2-O-17]thymine (1), [4-O-17]thymine (2), [2-O-17]uracil (3), [4-O-17]uracil (4), [2-O-17]cytosine (5), and [6-O-17]guanine monohydrate (6). Magic-angle-spinning (MAS) and static O-17 NMR spectra were acquired at 11.75 T for compounds 1-6, from which information about the O-17 chemical shift and electric field gradient tensors was obtained. Extensive quantum chemical calculations were performed at the B3LYP/6-311++G(d,p) level of theory for O-17 NMR properties in various molecular models. The calculated O-17 NMR tensors are highly sensitive to the description of intermolecular hydrogen-bonding interactions at the target oxygen atom. A reasonably good agreement between experimental solid-state O-17 NMR data and B3LYP/6-311++G(d,p) calculations is achievable only in molecular cluster models where a complete hydrogen-bond network is considered. Using this theoretical approach, we also investigated the O-17 NMR tensors in two unusual structures: guanine- and uracil-quartets.