There are a million Oxford abroad programs (OK, maybe not quite a million, but a lot).
The starting point is what YOUR college says about Oxford programs. Which ones are they affiliated with? What do they recommend? What do they say about applying?
My daughter's college offered five different options for studying at Oxford. Some through US college programs; some direct enrollment at Oxford colleges.
A 3.5 GPA was enough to be "competitive", but not guarantee acceptance. Full year junior year was most likely to be accepted, followed by spring semester junior year followed by spring semester sophmore year (very poor admissions odds). Her college would not allow a single fall semester at Oxford.