Originally Posted by Gokhan
Regarding the base oil in the Red Line High-Performance 5W-30, it's apparently roughly 82 - 87% PAO and 13 - 18% ester.
A recent MSDS showed < 90% PAO as a percentage of the base oil. Additives could take up to around 25%. So, it's mostly PAO. However, ester (POE) is not listed in MSDSs typically. So, the question remained how much ester is there in addition to the primary PAO base stock.
Oil-Club Russia got the FTIR oxidation number at 90%. Apparently, it's strongly correlated with the ester content in a VOA and 50% oxidation is roughly 7 - 10% ester. So, you are looking at about 13 - 18% ester, which makes sense. While that number seems small, it's bigger than for almost any motor oil, including the Motul oils marketed as being ester-based ("ester core"), which have around 5 - 7% ester (35% oxidation).
Surprisingly, the ester content in ILSAC varieties of Mobil 1 are very small, with the oxidation number being at 10%, so no more than about 1 - 2% of ester if any. European (ACEA) varieties of Mobil 1 such as FS 0W-40, ESP, and ESP X2 0W-20 show around 35% oxidation or 5 - 7% ester.
Amsoil Signature Series 0W-40 showed 60% oxidation number or more than 8 - 12% ester.
https://testoil.com/data-interpretation/fourier-transform-infrared-ftir/
"Oxidation mostly represents degradation of the fluid, but can also detect the presence of synthetic esters, which reveals some information regarding the base-stock formulation."
Now, here is the strange thing. The oxidation number Wear Check got for the TGMO 0W-20 SN sample I sent them in 2014 came out to be 68%. Does that mean that TGMO 0W-20 SN has 8 - 12% ester, similar to Amsoil Signature Series and only second to Red Line High-Performance? It would be remarkable if it did and it wasn't an artifact of WearCheck's FTIR algorithm.
Not a bad guesstimate.
Do AN's show up with an oxidation number in a VOA/UOA? Mobil tends to prefer ANs.