Maleic anhydride is produced by passing a C.sub.4 to C.sub.12 hydrocarbon stream together with molecular oxygen over a fixed bed containing a vanadium molybdate catalyst promoted with a novel cobalt tantalate having the formulaCoTa.sub.b O.sub.xwherein b is a number from about 1.0 to about 4.0 and x is a number from about 3.5 to about 11.0. The catalyst is prepared by calcining a slurry containing cobalt oxide and tantalum oxide, or their precursors, in at a temperature range from about 525.degree. to about 1200.degree. C. for about 1 to about 40 hours to obtain a cobalt tantalate, which is then slurried with a mixture of oxides of vanadium and molybdenum, or their precursors, dried, and then calcined at a temperature from about 300.degree. to about 650.degree. C. for about 0.5 to about 24 hours. A support can be used for the catalyst.