It has been discovered that para-xylene (PX) can be synthesized with improved selectivity by reacting an aromatic compound such as toluene and/or benzene with a reactant(s) from fuel syngas such as a combination of hydrogen and carbon monoxide and/or carbon dioxide and/or methanol,or methylating agents produced therefrom. The combination of the selective methylation technology and a source of fuel syngas creates several advantages including simplification of the selective methylation process and utilization of low cost feeds. The fuel syngas is used on a once-through basis.