V-51 NMR spectroscopy is used to investigate the thermodynamics of the reaction HVO42- + H+ reversible arrow H2VO4-. The enthalpy and entropy of this reaction are found to be very close to those of analogous reactions with phosphate and arsenate. This provides firm evidence that incorporation of water into the vanadate ion does not accompany the protonation of the dianion. Therefore, the tri-, di-, and monoanionic vanadates are all four-coordinate. The oligomerization reactions of vanadate are studied as a function of ionic strength and of pH and the results displayed graphically. The formation of the vanadate trimer and pentamer is examined in some detail, the identities of these materials are confirmed, and the apparent disappearance of the trimer at near-neutral pH is discussed.