Nanocrystalline SnO x particles (x ‫؍‬ 0 -2) were synthesized using tetramethyltin (Sn(CH 3 ) 4 ) vapor as the particle precursor reactant in hydrogen/oxygen/argon (H 2 /O 2 /Ar) flames. The particle composition and morphology were characterized using X-ray diffractometry, transmission electron microscopy, and nitrogen (N 2 ) surface adsorption. By controlling the concentration of oxygen in the reactant gases and the flame temperatures, metallic tin (Sn), tin monoxide (romarchite SnO), and/or tin dioxide (cassiterite SnO 2 ) were generated. The crystalline powders consisted of both discrete primary particles and agglomerates, with average primary particle sizes of 23-24 nm for SnO 2 and 69 nm for Sn (based on specific surface area measurements of bulk powders collected in the exhaust region of the flame). The compositional results were interpreted using equilibrium and detailed chemical kinetics models.