The oxides of Mg, Pb, Cr, La, Pr, Yb, Mn, Fe, Co, Zn, Zr, and Ce were studied as catalysts for the reactions of benzoic acid in the temperature range 523-723 K. All experiments were performed in a continuous how apparatus, at a total pressure of about one bar, with hydrogen as the reductant. The oxides studied could be subdivided into several groups according to their product pattern. The groups indicate the prevailing mechanism. The two basic mechanisms are : (i) Mars and van Krevelen (selective to benzaldehyde) and (ii) radical-like decomposition of benzoate. The highest yield of benzaldehyde can be obtained with oxides of high metal-oxygen bond strength.