Citibank offers an Amex card on AA. It charges the usual citibank 3% ftf (most use the AA mastercard I think). BA has an Amex card, at least one. Pen Fed has an Amex card, at least one.

Now the question of acquirer. Long long ago, once upon a time, merchants signed up with banks to accept whatever cc the bank accepted, then signed up with Amex to accept Amex cards, then signed up with Diners to accept DC until it was purchased by Citibank, then signed up with Discover when it came out.

But then as time marched forward, you signed up with a credit card processor to the point and I just use it as an example people signed up say with square.com and you could take all of them. In a few cases, there might be a slight difference in the discount rate if you took Amex. So when I take a credit card via my square account, for the 3 or 4 transacton I might do a year with or without a surcharge ... is square the acquirer? How many merchants, all kidding aside, have signed up with whatever company pushing dcc. Since it's all automatic today I assume that what happens in an Amex transaction the pos terminal will not flash a choice to be made of currency whereas with visa/mc it will.

I know the response is a bit convoluted to say the least but I guess it's not as simple as we would like to believe it is.