Costco, the second largest retailer in the U.S., has been a co-branded card partner of American Express since 2000. Amex/Costco TrueEarnings cards generated $79.79 billion in purchase and cash volume last year, equal to 7.8% of $1.023 trillion in global American Express card volume and 11.6% of U.S. volume of $688.10 billion. Total volume by Amex U.S. cardholders grew 8.0% last year. Costco will switch its issuing partner to Citi beginning April 1, 2016. Citi will issue only Visa brand credit cards for Costco. The card network and card issuing contracts were negotiated separately. Until ...