A catalytic dense membrane reactor allows to physically separate the oxygen feed from the reactant (hydrocarbon) feed with a catalytic membrane chosen among oxide ion conducting materials. The membrane plays a double role, it provides the oxygen needed for selective oxidation and acts as a catalyst. The catalytic properties of BIMEVOX (ME=Co, Cu, Ta) membranes were examined in the mild oxidation of propene and of propane. During the complex transient state observed when the surface is rough, the nature and distribution of products are different from those obtained with mirror-polished membranes in a former work. In particular, syngas is formed with propene as well as with propane, and it precedes the production of hydrogen and coke. The complex behaviour differs according to ME and seems to be related to the different nature of electron semi-conduction induced by each dopant. (c) 2006 Elsevier B.V. All rights reserved.