Fixed bed process for high viscosity index lubricant

In a process for the preparation of liquid hydrocarbons suitable as lubricant basestocks from alpha-olefin feedstock containing 6 to 20 carbon atoms, or mixtures of such olefins, comprising contacting said olefins under oligomerization conditions, at reaction temperature between 90.degree. to 250.degree. C. to vary product viscosity, and with a chromium catalyst on a porous support, which catalyst has been treated by oxidation at a temperature of 200.degree. C. to 900.degree. C. in the presence of an oxidizing gas and then by treatment with a reducing agent at a temperature and for a time sufficient to reduce said catalyst to a lower valence state to obtain an oligomeric liquid lubricant composition comprising C.sub.30 -C.sub.1300 hydrocarbons, said composition having a branch ratio of less than 0.19, weight average molecular weight between 420 and 18,000, molecular weight distribution between 1 and 5 and pour point below -15.degree. C., the improvement comprising;

• oligomerizing said olefins in a fixed bed reactor in contact with extruded reduced chromium oxide catalyst on a porous support at essentially constant oligomerization temperature and varying said olefin feedstock WHSV based on catalyst whereby said liquid lubricant hydrocarbon product viscosity can be selectively varied.