WO 3 nanofibers NFs, with diameter of about 150– 200 nm, were grown using the electrospinning technique starting from WCl 6 as tungsten source. The NFs were deposited onto a patterned substrate, for gas sensing measurements, and on a silicon substrate, for chemical and structural characterizations. The chemical composition of the NFs was determined by the x-ray photoemission spectroscopy, while high spatial resolution soft x-ray photoemission spectroscopy showed a chemical image of the NF. The gas sensing properties of these NFs were checked towards NO 2 and CO, showing a good response for NO 2 while no effect was observed for CO. © 2007 American Institute of Physics.