A process for the production of ethylbenzene by the ethylation of benzene in the critical phase over a molecular sieve aromatic alkylation catalyst. An aromatic feedstock having a benzene content of at least 90 wt. % is supplied into a reaction zone into contact with a zeolite beta alkylation catalyst having a silica/alumina ratio within the range of 20-500, specifically 50-150. The alkylation catalyst is a zeolite beta specifically a lanthanum-modified zeolite beta. Ethylene is supplied to the reaction zone to provide a benzene/ethylene mole ratio of 1-15. The reaction zone is operated under conditions in which benzene is in the supercritical phase to produce an alkylation product containing ethylbenzene as a primary product with heavier alkylated by-products of no more than 60 wt. % of the ethylbenzene. The alkylation product is recovered from the reaction zone and supplied to a separation and recovery zone to separate ethylbenzene from a polyalkylated component including diethylbenzene. At least a portion of the polyalkylated component is supplied to a transalkylation reaction zone containing a molecular sieve transalkylation catalyst. The transalkylation reaction zone contains a zeolite Y catalyst and is operated under liquid phase conditions.