Liquid state processing is the preferred route for the production of particulate reinforced Metal Matrix Composites (MMCs) due to the lower cost and the ability to form a variety of shapes.  However, the disadvantages of liquid state processing include the cost of the reinforcement, reaction between the particulate and liquid alloy, and the entrapment of gas or air bubbles during stirring of the reinforcement into the liquid alloy. In this work, a reactive gas is bubbled through an aluminum alloy melt. The reinforcing particles nucleate and grow directly from in-situ chemical reactions between molten metal and a gas source. Since the particles are formed in situ, they are thermodynamically stable and free of surface contamination, thereby yielding better interfacial properties that will not degrade during service.  The microstructure and properties of the resulting MMC are characterized.