Originally posted by Big Jim:
And until just the last year, Mobil 1 was only a synthetic blend.  The problem with a synthetic blend is the difficulty in controlling the base stock and producing a reliable oil that has consistent performance.. But hey, that was better than some others I can think of..
I guess you need to define your terms. From what I understand Mobil 1 has always been a full synthetic. Originally it was full group IV PAO and later became a blend of group IV and group V which it still is today.
If you use Castrol's definition of synthetic, the newest Mobil conventional oil would qualify, both use full group III base stocks.
Well John, based upon my course in lubricants, sythetic base oil Categories are group III with Sulfur <=0.03% and Saturates >=90%; all PAOs (Polyalphaolefins); and Group V.
I'll research my Mobil 1 info and get back to you. I do remember a change in the product that they did to upgrade from (I believe) a blend to a full synthetic, but for the life of me I don't remember what it was.. a senior moment.. 
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