Originally Posted by ahrz

Format of Amex card numbers :

AFAIK, "37" + 6 fields (named here A to F) :

37AA-BBCCCC-CDEEF

The "3" is the MII (Major Industry Identifier) for T&E cards, "37" reserved for Amex.


Field A : currency or country code
Field B : 88 for Centurion (and older Platinum accounts) , 99 for some corporate cards etc.
Field C : account number
Field D : card sequence number (from 1, incremented if card lost/stolen)
Field E : 00 for main card, 01 for first supplementary card, etc.
Field F : check number (using LUHN-10 algorithm)

These are guidelines, not absolute rules.
The US have many different values for Field A.
Field A = 46 for credit cards (not charge cards) issued in some countries, etc.