A premixed H2/O2/Ar flat flame operated in a low pressure reactor was used to investigate the influence of variation of experimental parameters on GeO/GeO2 nanoparticle formation. GeO as well as GeO2 are thermodynamically stable, and their appearance and disappearance respectively provides valuable information on oxidizing and reducing conditions in the flame. The reactor was fed with different concentrations of tetramethyl germanium [Ge(CH3)4], and operated for H2/O2 ratios between 0.6 – 1.3. The Pressure was varied between 25 – 55 mbar, while the gas velocity was also varied between 0.69 – 1.95 m/s. Furthermore, increasing pressure results in a corresponding reduction in mean particle diameter (particle size). An increase in oxygen concentration accelerates particle growth, for H2/O2 < 1, the colour of the GeOx powders is white indicating the preferential formation of GeO2. If the oxygen concentration decreases, the stoichiometry shifts to GeO represented by a colour transformation starting from white over grey to black. Transmission electron microscopy (TEM) and particle mass spectrometry (PMS) indicate the formation of particles with spherical morphology and mean diameters of 1.5 nm ? particle size ? 10 nm.