A process for producing oligomers from alpha-olefins, such as 1-decene, in which the olefins are oligomerized over a supported, reduced metal oxide catalyst from Group VIB of the Periodic Table to give oligomers with a branch ratio of less than 0.19. The catalyst, preferably a chromium/silica catalyst the catalyst can be regenerated to allow repeated recycling of the catalyst without a loss in yield of the oligomer product. The regeneration process comprises: (i) purging or stripping the deactivated catalyst with inert gas at elevated temperature to strip unreacted olefin and oligomer product from the catalyst; (ii) contacting the deactivated and purged catalyst with a stream of oxidizing gas while heating to elevated temperature to oxidize the metal component of the catalyst and remove carbonaceous deposits from the catalyst; (iii) cooling the oxidized catalyst and contacting it with a stream of reducing gas to reduce the metal component of the oxidized catalyst to a lower valence state. The oligomerization may be carried out at relatively high temperatures of about 90.degree. to 250.degree. C. to produce liquid lubricant products of high viscosity index, typically above 130, or at lower temperatures from about -20.degree. to about +90.degree. C. to product products of higher molecular weight which may be used as lubricant additives, e.g. VI improvers. The high molecular weight products are generally characterized by a branch ratio less than 0.19, a weight average molecular weight from about 15,000 to 200,000, a number average molecular weight from about 5,000 to about 50,000 and a molecular weight distribution from about 1 to about 5. They are also shear stable under high temperature, high shear rate conditions of 150.degree. C. and a shear rate of 10.sup.6 second.sup.-1.