American Express and Delta Air Lines have been co-branded credit card partners for 30 years. There are seven million Delta American Express consumer and business co-branded cardholders—about one-third of all members in Delta’s SkyMiles loyalty program. Last year, co-branded American Express cards generated $8.20 billion in revenue for Delta, an amount that exceeded its operating income tied to flights. Amex and Delta have just enhanced the value proposition of all Delta SkyMiles co-branded credit cards without raising annual fees. Card designs have also been updated. Basic, gold, ...