GGA+U calculation were performed for oxides of Ti, V, Mo, and Ce with the objective of establishing the best value of the parameter Ueff to use in order to match the calculated reduction and oxidation energies of each oxide with experimental values. In each case, the reaction involved the hydrogen reduction of an oxide to its next lower oxide and the formation of water. Our calculations show that the optimal value of Ueff required to match calculated and experimental values of the reaction energy are significantly different from those reported in the literature based on matching lattice parameters or electronic properties and that the use of these values of Ueff can result in errors in the calculated redox energies of over 100 kJ/mol. We also found that, when an element exhibits more than two oxidation states, the energy of redox reactions between different pairs of these states are described by slightly different values of Ueff.