When Forbes releases its annual ranking of the world's richest billionaires tomorrow (Wednesday), it appears likely Warren Buffett will once again come in behind his friend and online bridge partner, Bill Gates.

My extremely back-of-the-envelope calculation is based on big gains for shares of both Berkshire Hathaway and Microsoft over the past six months.

A year ago, Gates beat Buffett by $40 billion to $37 billion, ending the Omaha billionaire's one-year reign at the top of the global list.  Before that, Gates had been number one for the previous 13 years.

We got an update last September.  In its list of the 400 richest Americans, Forbes put Gates at the top with an estimated wealth of $50 billion.  Buffett was number two with $40 billion.

Over the past six months, Berkshire shares have gained almost 26 percent, with much of the gain coming in the last few months.  Microsoft hasn't done as well recently, but it had an early head start and the stock is up just over 17 percent.

Berkshire's 9 percentage point win should help Buffett close the $10 billion gap between him and Gates, but it probably won't be enough to win.

The simple math puts Gates at over $58 billion and Buffett at $50 million.

Nati Harnik / AP Bill Gates and Warren Buffett share a laugh while answering questions from students at the University of Nebraska-Lincoln's College of Business Administration, in Lincoln, Neb., in 2005.

Of course, it's not that simple.  Both men have sources of wealth other than the shares of their respective companies and their holdings change over time.  Forbes works hard on its estimates to include all the relevant factors, so we could be surprised when the list is revealed tomorrow at 6p ET.

But if I were a betting man, I'd put my money on Warren Buffett .. for second place.

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