When your metalworking fluid supplier starts talking about the base stock, the difference between naphthenic and paraffinic can be instantly confusing.  When I first heard the terms, I thought "Naphthenic" sounded a lot like "Napalm" and that "Paraffinic" must have some relationship to candle wax.  That's actually a decent guess if you are taking the SAT.  As a Metalworking Fluid Manager, you are expected to be a little more thoroughly informed.  Naphthenic base oils have long held a strong position in the metalworking fluids market.  Their better solubility and ability to form stable emulsions give them a clear advantage over paraffinic base oils.  The recent development of new additives for paraffinic oils has reduced the distinction between the two.  Swedish NYNAS R&D has conducted comparative studies to discover whether paraffin base oils are now equal players.  Read this article and you will sound a lot smarter than I did.