A set of four Viscosity Modifier (VM) or Viscosity Index Improvers (VII) and their blends in American Petroleum Institute (API) group I to group IV base oils have been studied for key performance properties that is thickening tendencies, viscosity index improvement, shear stability, and shear stability indices. All the four base oils have been characterized by Infra Red spectroscopy for their chemical composition. Gel Permeation Chromatography (GPC) has been used for characterizing the molecular weight distribution of VMs.