Production of high V. I. lubricating oil stock

In a process for catalytically hydrodewaxing a lubricating oil stock containing high pour point waxy paraffins by contacting the same in the presence of added hydrogen at elevated temperatures and pressures with a catalyst composition comprising a binder and a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12, the improvement which comprises carrying out said hydrodewaxing with said zeolite which has been silica-modified by the addition of at least 0.1% by weight silica to said catalyst from the reaction of said catalyst with silicones or silanes so as to enhance the selectivity of the catalyst for said high pour waxy paraffins and recovering a product having an enhanced viscosity index.