Group I base oils are the least refined of all the groups. With the use of solvents impurities are leeched out so it can be further processed. This method is quite standard and is the minimum when refining base oils. The mix after refining is made up from different hydrocarbon chains with little or no uniformity. While some automotive oils on the market use Group I stocks, they are generally used in less demanding applications. They are defined as having a viscosity index between 80 and 120 while the level of sulphur is larger than 0.03%.
