In recent years, several new types of base oils have become available on a global basis. These include high-quality mineral oils, specialty PAOs and vegetable oil-derived esters as well as recently introduced gas-to-liquid (GTL) base oils. Re-refined base oils are becoming more available also - are they as good as virgin base stocks? The currently-available collection of commercial base stocks feature a broad continuum of quality and, depending on their level of purity and viscometrics properties, are classified by the American Petroleum Institute as Group I, II, III, IV or V. With more types of base stocks being available and increasing pressure to improve lubricant performance, a tremendous amount of complexity has been added to the lubricant formulation process. This complexity provokes the question -- How can the industry deliver maximum value from this new generation of base oils? Answering that question requires an understanding of how base oil properties affect performance in finished lubricants and how formulations can be optimized to meet targeted specifications.