Brian,.....Oils ain't Oils Sol!
The aeroshell 15W-50 is a semi Synthetic aviation oil with the Lycoming additives. I am sure some others have a similar product, however this is the one I use for the availability of it.
I do not use it in the car, mind you get this, 12 x 946ml bottles of the aeroshell I think cost me $99, and 1 x 5L of Mobil 1 is about $65-70 I think, so something in aviation is not so bag after all!
J