As the world's third-richest person and most celebrated investor, Warren Buffett attracts a lot of attention. Thousands try to glean what they can from his thinking processes and track his investments.

We can't know for sure whether Buffett is about to buy Citigroup (NYSE: C) -- he hasn't specifically mentioned anything about it to me -- but we can discover whether it's the sort of stock that might interest him. Answering that question could also reveal whether it's a stock that should interest us.

In his most recent 10-K, Buffett lays out the qualities he looks for in an investment. In addition to adequate size, proven management, and a reasonable valuation, he demands:

1. Consistent earnings power.
2. Good returns on equity with limited or no debt.
3. Management in place.
4. Simple, non-techno-mumbo-jumbo businesses.

Does Citigroup meet Buffett's standards?

1. Earnings power
Buffett is famous for betting on a sure thing. For that reason, he likes to see companies with demonstrated earnings stability.

Let's examine Citigroup's earnings history:

Source: S&P Capital IQ.

Like much of the financial industry, Citigroup's earnings took a big hit in the 2008 financial crisis, culminating with nearly $21 billion in writedowns in 2007 and nearly $24 billion in trading losses in 2008, though the bank has been turning its operations around since.

2. Return on equity and debt
Return on equity is a great metric for measuring both management's effectiveness and the strength of a company's competitive advantage or disadvantage -- a classic Buffett consideration. When considering return on equity, it's important to make sure a company doesn't have an enormous debt-to-equity ratio, because that will skew your calculations and make the company look much more efficient than it is.

Since competitive strength is a comparison between peers, and various industries have different levels of profitability and require different levels of debt, it helps to use an industry context. Let's use a leverage ratio defined as assets divided by equity, which is commonly used for banks. In the United States, about 10 to 12 times is considered normal.

Source: S&P Capital IQ.

Buffett's company owns $11.6 billion of Wells Fargo stock and has been one of his longtime favorites because of its stable, low-cost deposit base and comparatively limited trading and investment-banking operations, which are managed to generate the highest return on equity. Even more impressive, Wells Fargo does so with the lowest leverage ratio of the bunch. Bank of America, another Buffett holding (the company gave him a special deal on the stock), once again had subdued earnings over the past year, this time on trouble with its stock investments, residential mortgage portfolio, and merger and restructuring charges from the crisis-era acquisitions of Countrywide and Merrill Lynch.

JPMorgan Chase, generally considered the most resilient of the troubled major Wall Street banks during the crisis, generated a reasonable return on equity considering how difficult 2011 was for its substantial trading and investment-banking units. Interestingly, Citigroup doesn't lag too far behind JPMorgan Chase in this area when you consider its smaller leverage footprint (and JPMorgan Chase's substantial derivatives exposure.)

3. Management
CEO Vikram Pandit has been at the job since 2007. He arrived at Citigroup a few months before that, when the bank bought Old Lane, a hedge fund he started in 2006.

4. Business
The banking industry isn't especially susceptible to technological disruption, but as the past several years have shown us, banks that delve too deeply into complexity and risk can be vulnerable to credit and economic cycles, as well as disasters of their own making. Again, megabank Wells Fargo is a major longtime Buffett holding, as are Bank of America preferred shares.

The Foolish conclusion
So is Citigroup a Buffett stock? Not especially, although it doesn't score as badly as one might think. Although it has tenured management and a technologically straightforward business, it doesn't particularly generate high returns on equity with limited debt -- nor, like much of Wall Street, has it generated consistent earnings over the past several years. However, if you're looking for some other bank stocks that might interest Buffett, check out The Motley Fool's "The Stocks Only the Smartest Investors Are Buying," which details some excellent bank stocks that share the characteristics of a Buffett bank investment. I invite you to read this special report for free.