This invention relates to a process for the production of lower aliphatic esters by reacting a lower olefin with a saturated lower aliphatic mono-carboxylic acid in the vapor phase in the presence of a heteropolyacid catalyst in a plurality of reactors set up in series such that the reactant gases exiting from a first reactor are fed as the feed gas to a second reactor and those exiting from the second reactor are fed as the feed gas to a third reactor and so on for the subsequent reactors. An aliquot of the reactant monocarboxylic acid is introduced into the feed gas to the second and subsequent reactors so as to maintain the olefin to monocarboxylic acid ratio in the feed gas to each of the second and subsequent reactors within a pre-determined range.