Abstract: A process for producing an vinylidene olefin of the formula ##STR1## where R.sup.1 and R.sup.2 are the same or different and are hydrogen or alkyl and m is an integer of from 0 to 18, with a catalytically effective amount of a mixture of i) an aluminum compound of the formula R.sup.4.sub.n Al(OR.sup.5).sub.p where R.sup.4 and R.sup.5 are the same or different and are alkyl, n is an integer from 0.75 to 2.75, and p is an integer from 0.25 to 2.25, the sum of n and p being 3, at a temperature of from about 120.degree. C. to about 200.degree. C. whereby a major amount of said vinylidene and deep internal olefin dimer is produced and only a minor amount of a beta internal olefin isomer.