Process for the preparation of hydrocarbons

A process for the preparation of a high-viscosity-index lubricating oil, wherein a feed mixture of carbon monoxide and hydrogen is converted into a mixture of hydrocarbons substantially consisting of linear paraffins, by contacting said feed mixture at elevated temperature and pressure with a catalyst comprising 3-60 pbw of cobalt and0.1-100 pbw of at least one other metal selected fom the group consisting of zirconium, titanium and chromium per 100 pbw of silica, alumina or silica-alumina carrier, which catalyst has been prepared by kneading and/or impregnation, that from the mixture of paraffins thus prepared a light fraction is separated which consists substantially of C.sub.10 -C.sub.19 paraffins, and that at least part of said light fraction is converted into a product comprising the desired high-viscosity-index lubricating oil by treating it at an elevated temperature with a peroxide of the general formula R-O-O-R.sup.1, wherein R and R.sup.1 represent alkyl, aryl or acyl moieties.