about 40-65% of ''m''-xylene and up to 20% each of ''o''-xylene, ''p''-xylene and ethylbenzene The ratio of isomers can be shifted to favor the highly valued p-xylene via the patented UOP-Isomar process or by transalkylation of xylene with itself or trimethylbenzene. These conversions are catalyzed by zeolites.