Abstract Cross sections of electron ionization of three isomeric xylenes, in an electron energy range of 10–200 eV, are measured. The maximum total cross sections are observed at 80-eV electron energy to be 2.24, 2.10 and 2.05 × 10−15 cm2 for m-xylene, p-xylene and o-xylene, respectively. The xylene compounds produce similar ion populations, with major product ions including C8H7,9,10+, C7H7+, C6H5–7+, C5H5+, C4H3+ and C3H3+. The similar ion populations can be explained through consideration of the fragmentation mechanism: essentially all fragment ions are formed via initial isomerization of the parent ions from the dimethylbenzene structures to the 7-methylcycloheptatriene structure.