The invention provides for a mineral insulating oil having a naphthenic base oil and a paraffinic base oil wherein the naphthenic base oil includes a ratio of total sulfur to basic nitrogen of less than about 80:1. The invention also provides for a mineral insulating oil having a naphthenic base oil, a paraffinic base oil, and an antioxidant agent wherein the naphthenic base oil includes a ratio of total sulfur to basic nitrogen of less than about 80:1. The invention also provides for a process for producing a mineral insulating oil including contacting a naphthenic base oil and a paraffinic base oil wherein the naphthenic base oil includes a ratio of total sulfur to basic nitrogen of less than about 80:1. The invention also provides for a process for producing a mineral insulating oil including contacting a naphthenic base oil, a paraffinic base oil, and an antioxidant agent wherein the naphthenic base oil includes a ratio of total sulfur to basic nitrogen of less than about 80:1.