Arene alkylation with ethene or propene over acidic zeolites has been investigated by quantum chemical calculations using a simplified zeolite model; a four T-atom cluster. Four different arenes are alkylated in this work: benzene, toluene, 1,3,5-trimethylbenzene, and pentamethylbenzene. The species resulting from toluene alkylation have been restricted to the para-isomers. Alkylation with propene formed n-propyl- and isopropylarenes. All the studied reactions are concerted reaction types with no intermediates between the alkene protonation step and ethyl/propyl-group formation on the arene. The reactions proceed by a simultaneous transfer of a proton from the cluster to the alkene, and formation of a C-C bond between the alkene and the arene. Dealkylations are also discussed, as elimination of alkyl groups from alkylarenes plays a central role in the methanol-to-hydrocarbons reaction. Comparisons between calculated and experimental values are done where possible. Computed energy trends are in good agreement with reported experimental data. The influence of different reactants on activation energies, reaction energies, and reaction paths is discussed.