Shares of Citigroup (NYSE:C) are surging today after the nation's third-largest bank by assets (click here to see a list of banks ranked by size) reported better-than-expected earnings for the first quarter of 2013. They're up by more than 1.8% roughly halfway through the trading day, making the bank one of the best-performing stocks on the S&P 500 today.

Coming into earnings season, analysts and investors were concerned that bank profits would not live up to expectations, given the continued economic malaise here at home and the financial turmoil in Europe. There's now a growing body of evidence that this fear was needless.

The good news started to roll in last week when JPMorgan Chase (NYSE:JPM) and Wells Fargo (NYSE:WFC) reported record quarterly profits. JPMorgan earned $6.5 billion in total. That equated to a 33% increase over the same quarter last year and, as you can see in the chart below, the best first quarter in the bank's history. Meanwhile, Wells Fargo earned $5.2 billion, closing the book on the California-based bank's "13th consecutive quarter of EPS growth and 8th consecutive quarter of record EPS."


Source: S&P Capital IQ.

Citigroup can now add its name to the list of stellar first-quarter performances. For the three months ended March 31, it earned $3.8 billion, a 30% year-over-year improvement. In addition, unlike JPMorgan and Wells Fargo, Citigroup grew its top line as well, increasing revenue by 6% over the same quarter last year. And for those of you watching mortgage origination volume, Citigroup followed JPMorgan's lead by underwriting 28% more home loans this year than last.

According to Citigroup CEO Michael Corbat, "During the quarter, we benefited from seasonally strong results in our markets businesses, sustained momentum in investment banking, continued year-over-year growth in loans and deposits in Citicorp, and a more favorable credit environment." He did go on to note, however, that "the environment remains challenging and we are sure to be tested as we go through the year."

Next up for the too-big-to-fail banks is Bank of America (NYSE:BAC), the nation's second-largest bank by assets. B of A reports earnings on Wednesday. And when it does, investors will be watching three things in particular: profits, mortgage origination volume, and expenses.

John Maxfield owns shares of Bank of America. The Motley Fool recommends Wells Fargo. The Motley Fool owns shares of Bank of America, Citigroup, JPMorgan Chase, and Wells Fargo. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.