Catalysts based both on nickel and ZSM-5 zeolites have been prepared and used for the dimerization of 1-butene. The reaction was performed at 40 and 80 bar and 100 to 200-degrees-C in a fixed-bed flow reactor with gas-chromatographic (GC) determination of alkenes product fractions characterized by their C atom number. Hydrogenation and GC analysis of the alkane C-8 isomers allowed determination of the degree of branching and of the linear isomers content of the C-8 fraction. The reactions detected were isomerization of 1-butene to 2-butenes, dimerization and further oligomerization of butenes. Favoured C-8 products were in every case several dimethylhexenes; however, under appropriate conditions, considerable fractions of linear octenes were obtained.