Cobalt ferrites (inverse spinel structures) were prepared by progressive heat treatments (270-600-1000 degrees C) in air of synthetic Fe : Co alkoxides of glycerol having different Fe : Co ratios. The XRD examination indicates that the crystallization of the cobalt ferrites is initiated at 270 degrees C and, thereafter, it strongly increases between 600 and 1000 degrees C. Moreover, at 1000 degrees C, XRD and chemical analyses show a shift of the resulting cobalt ferrite d-spacings to lower values when the ferrite contains more cobalt, suggesting that cobalt partially replaces iron in the spinel structure. At 1000 degrees C, the XRD lines of some coproducts like hematite and Co3O4 previously formed at 600 degrees C, either strongly decrease or disappear. The surface areas of cobalt ferrites range from 131 to 165 m(2)/g. Such high values are unusual for spinel oxides obtained by calcination at 1000 degrees C.