A process for producing an extender process oil having a kinematic viscosity at 100 °C from 16 to 30 cSt determined in accordance with ASTM D-445, an aniline point from 55 to 80 °C determined in accordance with ASTM D-611, a content of polycyclic aromatics of less than 3 %wt determined in accordance with the IP-346 method, a Tg minimum of -56 °C determined in accordance with DSC, and an aromatic content higher or equal to 24 % wt. determined in accordance with ASTM D-2140; the process comprising: a) providing a process oil educt that has a content of polycyclic aromatics from 3% w/w to 55 % w/w, determined in accordance with IP346, and a kinematic viscosity at 100°C from 16 to 250 cSt determined in accordance with ASTM D-445; the process oil educt comprises at least one of a primary extract or a secondary extract, the providing comprising a.1) obtaining the primary extract by solvent extraction of vacuum distillates in the lubricating base oil preparation; and a.2) obtaining the secondary extract by solvent extraction of the primary extract as obtained in a.1) with a solvent or a mixture of solvents, where at least one solvent is a polar extraction solvent; b) hydrotreating the process oil educt; wherein the hydrotreatment is carried out at a temperature from 300 to 380 °C, a pressure from 40 to 200 bar and a liquid space velocity from 0.1 to 1.5 h-1, to provide a hydrotreated oil stream; c) vacuum fractionating the hydrotreated oil stream obtained in step b), wherein the vacuum fractionating step is carried out in a vacuum tower obtaining a heavier fraction where the 5% according to ASTM D-2887 is from 400 to 465 °C and a gap equal or higher than -35 °C; being the gap defined as the difference between the 5% of the heavier fraction and the 95% of lights, the temperatures measured according to ASTM D-2887, to provide a vacuum fractionated hydrotreated oil stream having a viscosity at 100 °C from 16 to 60 cSt; and d) contacting the vacuum fractionated hydrotreated oil stream obtained in step c) with a solvent or a mixture of solvents, where at least one solvent is a polar extraction solvent, in an extraction unit and performing a liquid-liquid extraction process; wherein order of steps c) and d) may be interchangeable; obtaining the extender process oil which meets simultaneously all the above mentioned technical specifications. a) providing a process oil educt that has a content of polycyclic aromatics from 3% w/w to 55 % w/w, determined in accordance with IP346, and a kinematic viscosity at 100°C from 16 to 250 cSt determined in accordance with ASTM D-445; the process oil educt comprises at least one of a primary extract or a secondary extract, the providing comprising a.1) obtaining the primary extract by solvent extraction of vacuum distillates in the lubricating base oil preparation; and a.2) obtaining the secondary extract by solvent extraction of the primary extract as obtained in a.1) with a solvent or a mixture of solvents, where at least one solvent is a polar extraction solvent; a.1) obtaining the primary extract by solvent extraction of vacuum distillates in the lubricating base oil preparation; and a.2) obtaining the secondary extract by solvent extraction of the primary extract as obtained in a.1) with a solvent or a mixture of solvents, where at least one solvent is a polar extraction solvent; b) hydrotreating the process oil educt; wherein the hydrotreatment is carried out at a temperature from 300 to 380 °C, a pressure from 40 to 200 bar and a liquid space velocity from 0.1 to 1.5 h-1, to provide a hydrotreated oil stream; c) vacuum fractionating the hydrotreated oil stream obtained in step b), wherein the vacuum fractionating step is carried out in a vacuum tower obtaining a heavier fraction where the 5% according to ASTM D-2887 is from 400 to 465 °C and a gap equal or higher than -35 °C; being the gap defined as the difference between the 5% of the heavier fraction and the 95% of lights, the temperatures measured according to ASTM D-2887, to provide a vacuum fractionated hydrotreated oil stream having a viscosity at 100 °C from 16 to 60 cSt; and d) contacting the vacuum fractionated hydrotreated oil stream obtained in step c) with a solvent or a mixture of solvents, where at least one solvent is a polar extraction solvent, in an extraction unit and performing a liquid-liquid extraction process; wherein order of steps c) and d) may be interchangeable; obtaining the extender process oil which meets simultaneously all the above mentioned technical specifications.