The Raman spectra of aqueous vanadium (V) solutions at different pH values, ranging from 13.1 to 7.0, are presented. The dominant bands in the range 700–1100 cm−1 are assigned to the VO symmetrical stretching of the different oligomers, using additional information from 51V NMR spectra and empirical models. The effects of pH, concentration and ionic strength on the oligomerization equilibria are discussed. The ionic strength is found to affect significantly the oligomer composition of vanadate solutions, which is of interest in biochemical and biological studies.