Look at the first digit of the credit card number, which identifies the broad category of the industry that issued the card. The most common first digits are 1 and 2 for airlines, 3 for travel and entertainment, 4 and 5 for banking and financial, 6 for merchandising and banking, 7 for petroleum and 8 for telecommunications. For example, a credit card number beginning with 7 is probably an oil company or gas station card.
Count the number of digits in the credit card. Cards with 14 digits are typically Diner's Club and cards with 15 digits are typically American Express or older JCB credit cards. Most other major types of credit cards have 16 digits.
Match the first few digits of the credit card number to one of the major credit card issuers if possible. Discover cards begin with 6011 or 65. MasterCards begin with a number from 51 to 55. American Express cards begin with 34 or 37. JCB cards begin with 2131, 1800 or 35. Visa cards all begin with 4.