Controlled oligomerization of olefins

In a process for preparing oligomers of aliphatic olefins having from about 6 to about 12 carbon atoms in the presence of boron fluoride promoted by a minor amount of alcohol or water, the improvement which comprises conducting the reaction at a temperature between about 0.degree. C and about 60.degree. C in the presence of a catalyst modifier which controls the reaction to reduce formation of oligomers higher than the trimer;

• said modifier being methyl or ethyl ester of a mono carboxylic acid having 2-5 carbon atoms in an amount of about 0.001 moles to about 0.075 moles of ester per mole of said alpha olefin.