Larry, to prove what I said in an earlier reply:

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This whole idea of Mobil One not being synthetic might possibly be nothing more than idea of the marketing people for one of their competitors.
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I disagree here. Mobile 1 WAS NEVER a 100% synthetic because the 15 - 20% of the additive was dissolved in a dino carrier oil (full PAO synthetic oil cannot dissolve the additives). It was right on the Mobile 1 bottle of the old formulation.
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The FAQ below from Mobile 1 Website says it clearly in their own words that Mobile 1 has mineral oil in it:

http://www.mobil1.com/index.jsp

Q:
Why do fully synthetic oils still contain small amounts of mineral oil?

A:
All motor oils contain additives that provide extra protection against wear, corrosion and engine deposits. These additives are dispersed in mineral oil carriers that are mixed in small amounts into the synthetic oil. The carrier oils amount to a very small percentage of the finished motor oil.