We present gas-sensing performance of two dimensional tungsten oxide nanosheets (2D WO3-1) with extraordinary selectivity and sensitivity to NO2. The nanosheets were synthesized using wet chemical synthesis. Material characterizations including transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD) were carried out to ascertain morphology and compositional properties showing that as sensitized nanosheets are substoichiometric. The developed sensor's performance was compared to that of the full stoichiometric based sensor, showing a substantial difference in response factor as well as reaction kinetics in response to NO2 gas. The WO3−X based sensor showed a large response to NO2 at low parts per billion (ppb) which is at least 3 times greater than that of the stoichiometric sensor. Both stoichiometric and substoichiometric based sensors are selectively responsive to NO2 and have a lower detection limit of less than 20 ppb.