American Express introduced a new credit card.

The company unveiled its new Optima credit card that, unlike its existing cards, would allow customers to pay only part of their monthly account balance. Optima’s interest rate on unpaid balances is based on the prime rate, and currently would be 13.5%. Optima will be available, in green, gold and platinum versions, only to credit-worthy American Express cardholders of at least a year. It carries a $15 annual fee, and has a 25-day grace period--the delay before interest charges begin mounting on unpaid account balances.