A set of Mo, V, and W mixed-oxide samples with additives P and Cs showing high performance in selective partial oxidation of propene is studied by means of elemental mapping and crystal structure determination using scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) as supplement to XRD measurements which are insufficient for phase determination. The set is divided into two subsets of samples denoted A and B, where subset A samples show the highest performance in selective partial oxidation of propene. These high-performance catalysts are all predominated by structures of the Mo5O14 type in contrast to a negligible amount of the orthorhombic MoO3, which is known to favor total oxidation. (C) 2004 Elsevier Inc. All rights reserved.