A process for the production of petroleum sulfonates from lubricating oil extract fractions wherein a primary extract-solvent mixture, preferably substantially free from water, is cooled to a temperature at least 25.degree. C. below the extraction temperature to form two immiscible liquid phases comprising a secondary extract phase which is richer in aromatic hydrocarbons than the primary extract and a secondary raffinate phase which is poorer in aromatics than the primary extract. The secondary raffinate is sulfonated and the unsulfonated fraction returned to the separations process.The process results in improved yields of petroleum sulfonates with lowered SO.sub.3 consumption and less by-product sludge than conventional processes in which the entire extract fraction is sulfonated.