Water reacts on molecular sieve catalysts used in oligomerization reactions and forms oxygenated compounds, in particular organic acids that may cause corrosion problems downstream of the reactor, in particular in distillation tower overhead systems and downstream thereof. A lowering of the presence of water in the feed prior to contacting thereof with the molecular sieve brings a significant reduction in corrosion downstream. At the same time, it has a significant beneficial effect on catalyst activity and brings a significant extension of catalyst life. Lowering water in the feed is particularly effective when organic nitrogen-containing Lewis bases are present in the feed, even at low levels.