Q.Getting olive trees to produce fruit.
My wife planted four olive trees as an experiment to see if they would survive our South Carolina winters. They have.
However, we have gotten no olives. The trees are 9 years old. We no longer know which varieties we have or if we don’t have the correct “sexes” .
Is our situation hopeless or are tests available or is our climate/soil just wrong?
Thank you for any help you might provide.

It seems that olives were actually grown commercially in South Carolina in the 1800s, so your climate should be fine for them. It could indeed be a problem with the varieties needed to cross-pollinate. Is the tree producing flowers? If not, first, see this article to check whether there might be any other problem:
https://www.gardeningknowhow.com/plant-problems/environmental/plant-not-blooming.htm
These articles have information about the varieties needed for cross-pollination. You may also want to ask a university extension agent whether there is a way to check what variety you have.
http://edis.ifas.ufl.edu/ep515
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=21374