The invention relates to a process for producing base oils, comprisings the steps where feedstock selected from ketones, aldehydes, alcohols, carboxylic acids, esters of carboxylic acids and anhydrides of carboxylic acids, alpha olefins, metal salts of carboxylic acids and corresponding sulphur compounds, corresponding nitrogen compounds and combinations thereof, is subjected to a condensation step and subsequently subjected to a combined hydrodefunctionalization and isomerization step.