A rational approach to control the behavior of nickel(II) ion-exchanged silica-alumina oligomerization catalysts has been attempted. Emphasis has been placed on securing higher selectivities to 1-alkenes from the oligomerization of ethene, with data being presented for 1-hexene. A key challenge is to reduce the relatively high rate of double-bond shift which leads to the formation of internal alkene products. One of the most effective means of inducing favorable changes in the 1-hexene content of the hexane fraction appears to be an increase in the time-on-stream, though this aspect is not observed for all catalysts studied. Addition of nickel ions in excess of those introduced by ion-exchange, addition of potassium ions, and changes in the Si/Al ratio of the support are further variables investigated. These variable do not, for each one studied, lead to dramatic changes in the selectivity, but the combined effect of appropriate adjustments in these factors do give some improvement. In addition, the total nickel ion content influences the carbon number-based product distribution, with the highest hexene selectivity being found with catalysts containing 1.5 mass% Ni2+. (C) 2002 Elsevier Science B.V. All rights reserved.