A.k.a. mixed xylenes or MX. A benzene co-product usually extracted or distilled from reformate or created by toluene disproportionation. Xylene is an aromatic comprised of three isomers: p-xylene, o-xylene, and m-xylene (metaxylene).  Mixed xylenes vary in composition and include a variety of impurities with ethylbenzene being the largest. The mixture is processed to concentrate and separate the isomers with p-xylene being the most desired product. Mixed xylenes are used directly as an octane enhancer in gasoline or as a solvent.