Synthetic does not have the meaning it used to. Used to be a synthetic oil was either group V esters or group IV PAO. In the late 90's Castrol changed its formula from PAO to hydro-cracked group III oil which is mineral based. It lead to and industry fight mostly between Mobil and Castrol over the definition of synthetic. Mobil objected to classifying group III as synthetic, but eventually lost out. Just FYI it was not a lawsuit that occurred but a complaint filed with the National Advertising Division of the Better Business Bureau. They ruled that Castrol was not falsely advertising as Mobil had asserted.
Fast forward to today and most "synthetic" oils on the shelf are actually mineral oil based. A few of the boutique oils are true synthetic as are some of the European oils. AFAIK Germany and a few other companies only allow the word synthetic on "true" synthetics.
No need to worry though, the oil that is on the shelf today is great stuff. The refiners have progressed their science so far that even mineral based oils are lasting 15k or more. So as said earlier synthetics are about marketing and not performance.
I hope I got the details right LOL
