A nuclear magnetic resonance study of the F19 resonance in a single crystal of KNiF3 is reported. The internal fields at the fluorine nuclei were measured. Interpretation of the measured fields showed that the spin densities in the fluorine 2s and 2pσ orbitals were (0.538+/-0.05)% and (3.78+/-0.2)%, respectively. A comparison with the KMnF3 measurements, where pπ interactions are allowed, indicated the importance of pπ bonding in these crystals. It is shown that only a model which allows the 2s, 2pσ, and 2pπ electrons individual degrees of covalency can explain the observations.