Hex-1-ene in octane solvent was oligomerized in a down-flow tubular reactor holding a fixed catalyst bed at temperatures of 80-300 degrees C and a pressure of 5 MPa. Ultrastable Y (US-Y), hydrogen beta, and MCM-22 zeolites, MCM-41, silica-alumina and silica-magnesia co-gels, and gamma-alumina were evaluated as catalysts. The reaction products obtained are composed of hexene dimers and trimers, cracked products, C-6 alkanes, and isohexenes. The catalytic activity of the mesoporous silica-alumina co-gels and MCM-41 is very similar to that of beta, MCM-22, and US-Y zeolites. The oligomerization process occurs in the mesopores and on the exterior surfaces of the zeolite crystals. In the micropores of zeolite beta and US-Y: the hexenes undergo dimerization-cracking reactions generating isohexenes and cracked products. In MCM-22, having narrower micropores, these cracking reactions are suppressed. MCM-22, MCM-41, and silica-alumina co-gels lacking microporosity are the most selective hexene dimerization catalysts. (C) 1999 Academic Press.