So I don't think you need an Oyster card anymore - if you have Apple
Pay or Android Pay, or an NFC bank card, it should work fine.
Certainly that's what I use around the tube these days.
Dave is right. I have used my US issued Amex card on the tube and it
worked impressively well. They charged me once a day for the total of my
trips on that day.
Be sure your card has a contactless chip since most US cards don't. The
logo is a set of concentric arcs, sort of like a simplified wifi logo.
R's,
John
PS: On the other hand, if you are an auld pharte with a Senior Railcard,
you can only tie that to a physical Oyster card, not a credit or debit
card.
https://oyster.tfl.gov.uk/oyster/entry.do
https://tfl.gov.uk/fares-and-payments/