In this paper, we report the synthesis of one-dimensional zinc oxide (ZnO) nanostructures and the impact of their morphology on oxygen gas sensing properties. The nanostructures were synthesised via chemical vapour deposition using direct oxidation in an electrical furnace. Structural characterisation of the samples was performed with a field emission scanning electron microscope (SEM) and X-ray diffraction (XRD) methods. The SEM images revealed the formation of different sized nanowires, nanorods and nanoflower structures, and the XRD pattern showed hexagonal structures, without any impurities. The gas sensing properties of samples grown on silicon and alumina substrates were measured in different conditions. The samples grown on the alumina substrate showed better gas sensing properties than those grown on the silicon. To determine the optimal sensitivity, the oxygen gas sensing properties of the ZnO nanostructures were measured at different temperatures and gas flows. These nanostructural gas sensors showed high sensitivity at temperatures close to ambient. The effect of the morphology of ZnO nanostructures on their oxygen sensing properties was compared. Between the different synthesised nanostructures, ZnO nanowires exhibited the highest gas sensitivity.