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Wells Fargo (NYSE:WFC) has chalked up many accomplishments over the past decade, and it could soon add one more. Given its average annual growth rate over the last three years, Wells Fargo is poised to surpass Bank of America (NYSE:BAC) in size. That would make Wells Fargo the second-biggest bank in the country.

Consider this: Wells Fargo's balance sheet grew by 10% in the latest quarter compared to the same period last year. Bank of America's was up only 2%. And neither was a fluke. If you look back over the past three years, Wells Fargo's average annual growth rate comes out to 9% versus Bank of America's 0%.

This has rapidly closed the size gap between the two banks. It's almost hard to believe, but going into the crisis, Bank of America was triple the size of Wells Fargo. In the fourth quarter of 2007, Bank of America had $1.7 trillion in assets on its balance sheet. Wells Fargo's assets added up to only $575 billion.

But Wells Fargo is now nipping at Bank of America's heels. At the end of the second quarter, Bank of America was only 16% larger, holding just under $300 billion worth of assets more than its rapidly growing counterpart. To put that in perspective, Wells Fargo grew its loan portfolio in the same quarter by $80 billion over the year-ago period.

Data source: Chart by author.

Two things enabled Wells Fargo to narrow this gap. The first was that Bank of America had to retreat and retrench in the wake of the crisis. Its acquisition of Countrywide Financial's crushing legal liabilities, combined with its own record of handing out credit cards to basically anyone with the strength and wherewithal to slide one through a credit card reader, have cost the North Carolina-based bank $200 billion in added expenses over the past eight years.

The net result is that Bank of America has had to focus almost exclusively over the past decade on cutting expenses and firming up its capital base. It's sold off dozens of businesses, curtailed the number of financial products and services that it offers, and disposed of many tens of billions of dollars' worth of delinquent loans. In doing so, Bank of America shrank from a $3 trillion bank, in the immediate wake of its 2008 Merrill Lynch acquisition, to $2.2 trillion today, CEO Brian Moynihan explained in a Thursday morning interview on Bloomberg Television.

Wells Fargo, meanwhile, has gone in the opposite direction. Its 2008 acquisition of Wachovia more than doubled its size, and it has continued to grow organically ever since. In fact, it already has the biggest loan portfolio in the industry, surpassing even JPMorgan Chase, the nation's biggest bank by assets.

By projecting their recent growth trends forward, you can get a sense for how quickly Wells Fargo could eclipse its one-time California neighbor. By my math, it would happen in two years. At that point, Wells Fargo would narrowly edge out Bank of America with $2.24 trillion of assets.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.