Kamele0N,
Speaking about the subject touched in your post I think that it all depends.
Yes, big companies like BP, Shell, etc are extracting the mineral oil from the planet and perhaps they are capable of choosing from many different flavors. On the other hand, if they extract a lot they need to sell it, so they might be only interested in volume of sells rather than the quality of base stocks.
Small companies may choose from different base stocks selecting the best performance/price ratio and if they are in premium segment they can choose the best stocks.
A typical example, is for example Gazprom from Russia. Have you heard about any good oils made by Gazprom which are as good as say Liqui Moly? They are doing some oils, but those are inferior to Liqui Moly (LM) and that's because LM can choose better stocks and do a better chemo.
The bottom line is that one needs to see reviews of oils and judge by performance results and not by how much company is pumping the oil out of the planet.