Originally Posted by CT-UK
With Amex charge cards you are not allowed to pay more than your statement i.e. you are not allowed to go into credit. (This is the case in the UK). This is why if you go to a AMEX shop to pay you must have the statement with you.
This not always true.
If you settle your account using wire transfer, you are allowed to pay more
(for instance, for the UK managed International Currency cards).
Amex Shops accept payments without statement, but it's certainly limited
to a few thousand $.