Magnetic nanocrystalline materials cover a broad spectrum of industrial applications. Here we present the optimization of the traditional reverse micelle process, which is a surfactant-stabilized water-in-oil microemulsion synthesis technique, to produce different phases of magnetic iron oxide in bulk. The size of the nanoparticles produced was carefully tuned and greatly depended upon the synthesis conditions such as pH, temperature, concentration of reactants, and the water-to-surfactant ratio. The thermal stability of the synthesized iron oxide particles was investigated using the x-ray diffraction technique. The maghemite to hematite transformation took place at ~550°C and 11 nm crystallite size. Transmission electron microscopy and Williamson- Hall analysis from x-ray diffraction showed that the crystallite size ranged from 5-50 nm. The particle size measured from dynamic light scattering was found to be between 50 and 500 nm. The effectiveness of various washing media was also demonstrated by Fourier transform infrared spectroscopy and energy dispersive spectroscopy measurements.