During the course of a study on the clustering of WSe and WS mixtures in the gas phase using laser desorption ionization (LDI) mass spectrometry, we observed several anionic WO clusters. Three distinct species, W 6O19, W13O29, and W 14O32, stand out as intense peaks in the regular mass spectral pattern of tungsten oxide clusters suggesting unusual stabilities for them. Moreover, these clusters do not fragment in the postsource decay analysis. While trying to understand the precursor material, which produced these clusters, we found the presence of nanoscale forms of tungsten oxide. The structure and thermodynamic parameters of tungsten clusters have been explored using relativistic quantum chemical methods. Our computed results of atomization energy are consistent with the observed LDI mass spectra. The computational results suggest that the clusters observed have closed-cage structure. These distinct W13 and W14 clusters were observed for the first time in the gas phase. © 2010 American Chemical Society.