Just an FYI, the majority of the oil used in the US comes from Canada. I keep seeing posts about people worrying about middle east oil, but percentage wise it does not make up a large part of total oil used in the US. Canada is #1, Mexico #2
Here is a link to an AMSOIL site that I found searching the net. I sounds like AMSOIL is not petroleum based. You might be able to ask them specific questions on that site?
This will tell you a great deal about how true synthetic oil is made. Be aware though that certain oils labeled "synthetic" are, in fact, derived from petroleum.