With the latest earnings from Wells Fargo (NYSE:WFC) and Citigroup (NYSE:C) in the books, it may come as no surprise Wells Fargo topped Citigroup on a total earnings basis. But what may come as a surprise is one critical area in which Wells Fargo has begun to take the lead.

Source: Flickr / Matthew Devalle.

The key growth industry
Citigroup has long been one of the leaders in the credit card landscape, and 2013 was no exception. In the year its global credit card operations alone delivered a staggering $21.1 billion in revenue to the bank. Yet Wells Fargo has progressively been expanding its credit card business, and the results from the first quarter reveal things may have begun to come to truly take shape and could be a sign of great things to come.

It's important to note each bank is different in how it reports its earnings, so getting an apples to apples comparison in specific businesses can be difficult at times. However, there is enough evidence to suggest Wells Fargo has indeed begun to take critical steps forward.

A glance at the top line reveals Wells Fargo witnessed its card fees rise by 6% from the first quarter of 2013 to $784 million in the first quarter of this year. And while Citigroup only reports its total revenue -- which encompasses interest income as well -- it actually witnessed its North American Citi-branded cards revenue stay flat at $2 billion.

Yet perhaps even more interesting was Wells Fargo saw the total purchase volume on its credit cards rise by 14% year over year, whereas Citi only saw its rise by 5%. Like the total revenue, Citigroup still has a commanding lead with over $56 billion in total purchase volume compared to $13 billion at Wells Fargo, but this still displays the strong growth exhibited by Wells Fargo.

In addition to the strong growth in both revenue and total card use exhibited by Wells Fargo, the bank also reported it was able to expand its card network to 38% of its retail banking customers, versus 34.1% in the first quarter of last year. CEO John Stumpf also noted the Wells Fargo witnessed, "record new account growth," in the quarter.

The takeaway
Knowing the reality that Citigroup's purchase volume was more than quadruple that of Wells Fargo, it would be difficult to suggest Wells Fargo now has a more dominant or important credit card business than Citigroup.

However, metrics like those mentioned above reveal both the reality that Wells Fargo has displayed both strong performance and has ample room for growth, which could be to the delight of its already happy shareholders.