A normal 1-alkene containing 3-8 carbons is coupled with itself, another such alkene, or ethene in the pres­ence of a supported alkali metal as a catalyst and 10-100 mol %, based on the amount of alkali metal catalyst, of an alkali metal hydroxide as a co-catalyst; the support being a silica having a surface area not greater than 5 m²/g. In preferred embodiments of the invention, the alkene is propene or a mixture of propene and ethene, the alkali metal is potassium or a potassium alloy, and the co-cata­lyst is potassium hydroxide.