Abstract It is confirmed that the Zachariasen equation is more accurate than the Brown-Shannon equation. Moreover, it is shown that, given the value of the parameter R1 relative to the MoO bond in MoO6 octahedra, the calculated valence of molybdenum in Mo(V)O6 octahedra remains very close to 5 v.u. by varying the other bond parameter B in a wide range. For other oxidation states of molybdenum in MoO6 octahedra, the difference between the calculated valence and the formal oxidation state shows different types of dependence on B. These behaviours could explain some errors in valence data of the literature. The parameters for the MoO bond in MoO6 octahedra are recalculated as R1=1.8788 A and B=0.3046 A for all molybdenum oxidation states from +3 to +6.