Citi's personal and business Costco credit cards allow cardholders to earn 4% cash back on gas worldwide for the first $7,000 spent, then 1% thereafter; 3% cash back on restaurant and travel ...

In its Q4 2016 earnings release, Citi posted 8% overall revenue growth on a constant-currency basis. The Costco portfolio appears to be a major driver of Citi’s overall growth right now.

Corporate logos are seen on the rear of a Costco membership card/American Express credit card in this photo illustration taken in Toronto, Ontario February 12, 2015. REUTERS/Hyungwon Kang ·Reuters ...