I am an american student with a German citizenship and considering applying to Oxford and Cambridge. Would I be able to apply as an EU student under my German citizenship?
I would think so, though you should ask UCAS for clarification.
You don’t apply as a citizen of any place: the only two things that citizenship matters for are visa and fees.
Your German citizenship means that you don’t need a visa.
Your American residency means that you are an international student for fees (unless you are in the US b/c your family has been posted there on behalf of your government, such as diplomatic service).
In the UK, fee status is based on tax-residency, not citizenship. Think of it in terms of in-state and out-of-state tuition: doesn’t matter what state you were born in, it matters what state your family pays taxes in now.
ps, b/c somebody else is going to point this out to you anyway: you can only apply to Oxford OR Cambridge, not both.
You would only be able to pay EU fees if you and your family are resident in the EU for the three years preceding starting the course.
Complete guide to fee status: http://www.ukcisa.org.uk/International-Students/Fees–finance/Home-or-Overseas-fees/England-Higher-Education/