Together these data provide strong evidence that the barium titanium oxyhydrides have a bandstate electronic structure and the NMR shift corresponds to the Knight shift. Previously, a number of NMR investigations had observed negative 1 H or 2 H shifts and associated it with the metallic character of the material. Misaki et al. , in correspondence with the current study, demonstrated an essentially linear relation between the hydride content in BaTiO 3 x H y and the Knight shift. In contrast, Guo and coworkers detected different hydride isotropic shift values for samples with similar hydrogen content. This discrepancy can be explained by the formation of oxygen vacancies, which also introduce electrons in the 3d-band of Ti. Indeed, the Knight shift becomes more negative in the reported materials with increasing oxygen vacancy concentration, confirming the proposed correlation between number of conduction electrons and the NMR shift. Finally, we call attention to the lineshapes of the MAS spectra in Fig. ) and of the static shift projection in Fig. ) both of which display a skew towards shifts frequencies. This can be explained by different crystallites in the sample having distinct hydride or oxygen vacancy concentrations, which lead to a distribution of Knight shifts.