The reduction in oxygen contamination levels in organometallic precursors has been established as a key requirement in the metal organic vapour-phase epitaxy (MOVPE) of high brightness light emitting diode (LED) and laser devices. A number of different volatile oxygen-containing impurity species have been identified, and both physical and chemical techniques have been developed to eliminate them from a wide range of source materials to produce the next generation grade of high-purity products. In this study conclusive growth results are presented to highlight the significantly improved quality of device structures obtained when higher purity oxygen-free precursors are employed.