A process for the preparation of linear alpha olefins having 2n carbon atoms from linear alpha olefins having n carbon atoms comprising the steps of (a) dimerizing a linear alpha olefin having n carbon atoms in the presence of a dimerization catalyst to produce a linear internal olefin having 2n carbon atoms; (b)(i) reacting the linear internal olefin having 2n carbon atoms produced in step (a) with a trialkylaluminium compound in the presence of a catalytic amount of an isomerization/displacement catalyst in order to cause isomerization of the linear internal olefin and to displace alkyl group(s) from said trialkylaluminium compound to form an alkyl aluminium compound wherein at least one of the alkyl groups bound to aluminium is a linear alkyl which has been derived from the isomerization of said linear internal olefin; and (b)(ii) reacting said alkyl aluminium compound with an alpha olefin optionally in the presence of a displacement catalyst so as to displace said linear alkyl from said alkyl aluminium compound to form a linear alpha olefin having 2n carbon atoms.