I just saw this very nice article on base-oil demands by API SP/ILSAC GF-6 and GM dexos1 Gen 3. It is an interesting read indeed. The synthetics are coming by Caitlin Jacobs -- Lubes'n'Greases (PDF version with figures) The synthetics are coming by Caitlin Jacobs -- Lubes'n'Greases (HTML version without figures) One of my conclusions in the past was that the base-oil quality is inversely proportional to CCS x Noack for API Groups I - IV, including GTL. For finished 0W-20 oils, I used the following formula as a base-oil quality index (BOQI): BOQI = 3,500,000 / (CCS x Noack) (Used for finished 0W-20 oils, CCS measured at -35 Â°C) ExxonMobil has introduced a new KV100 = 3.39 cSt PAO base stock with CCS = 623 cP and Noack = 12.5%. Their old KV100 = 4.10 cSt PAO base stock has CCS = 1,430 cP and Noack = 12.4 cP. These are the base-oil quality indexes for the old and new PAO base stocks: BOQI (new 3.39 cSt PAO) = 449 BOQI (old 4.10 cSt PAO) = 197 They measured the oxidation times for the two base stocks: Oxidation time (new 3.39 cSt PAO) = 88 minutes Oxidation time (old 4.10 cSt PAO) = 41 minutes The base-oil quality is most closely related to the oxidation time. BOQI for the new PAO base stock is 2.28 times BOQI for the old PAO base stock. The oxidation time for the new PAO base stock is 2.15 times the oxidation time of the old PAO base stock. Therefore, BOQI is indeed directly correlated with the base-oil quality. In summary if you want to maximize the base-oil quality, you need to minimize both the CCS and Noack. For this reason 0W-16 and 0W-20 oils have higher base-oil quality than thicker oils such as 5W-30. Since the Noack is fixed by the industry and OEM specs, the base-oil quality increases as the oil gets thinner and the CCS decreases. For better deposits control (including on GDI intake valves) and longer OCIs, use the thinnest SAE viscosity grade recommended by your owner's manual and do not use a higher viscosity than recommended.