The new Form 13Fs are here! The new Form 13Fs are here!

Yes, Fools, it's that most wonderful time of the year (times four). The time Warren Buffett's Berkshire Hathaway (NYSE:BRK-A) releases its quarterly report of changes in stock holdings. This is our chance to sneak a peek within the mind of the world's most famous investor, and catch a glimpse of what he's thinking -- and Buffett didn't disappoint.

On Tuesday, Berkshire filed its quarterly Form 13F-HR with the SEC, revealing a multitude of tweaks and fine-tunings to the Master's portfolio. In it, we see that Buffett is ...

  • Continuing to sell down stakes in CarMax and ConocoPhillips.
  • Paring back his holdings in Exxon Mobil (NYSE:XOM), WellPoint (NYSE:WLP), and Procter & Gamble (NYSE:PG).
  • Closing out his positions in Norfolk Southern and Union Pacific entirely.

So … does Warren Buffett hate railroads?
Hardly. As you've no doubt heard by now, Berkshire is actually swallowing rival railroad Burlington Northern Santa Fe (NYSE:BNI) whole -- Buffett's biggest acquisition ever by a long mile.

This being the case, I suspect shareholders of Norfolk Southern and Union Pacific needn't worry that Buffett sees something wrong with their stocks. The more logical conclusion is that since he's placed his biggest bet on Burlington, he sees a conflict of interest in owning its rivals as well and that perhaps the Feds would, too. Or perhaps he simply believes that if the railroad he already owns is best-of-breed, there's little logic in diluting his success in owning it, by also placing bets on the railroads that he thought less worthy of his money.

You can make a related argument about Buffett's several non-railroad sales. Take the sales at Procter & Gamble for instance. Buffett's on record praising Procter & Gamble's purchase of Gillette. If he's selling down his stake in the stock, this could be happening out of a simple desire to raise cash, so that Berkshire need not take on more debt than necessary to fund the Burlington buyout

And yet, if Buffett's only purpose in selling off these stocks was to free up cash for the Burlington acquisition … that still wouldn't explain why he decided to increase his position in Wells Fargo (NYSE:WFC) and Wal-Mart (NYSE:WMT) -- or double his stakes in Iron Mountain and Republic Services. All of which he's done over the past three months. So clearly, raising cash wasn't the sole reason for Buffett's shifting his portfolio around.

And what about the oil?
That's the really interesting question this week. Buffett's sales of Exxon Mobil and ConocoPhillips stock do seem to suggest a bearish view on the near-term prospects for big oil. In fact, Buffett admitted last year that he made a mistake in buying Conoco at the top of the oil boom. It's curious, therefore, that with oil now trading in the $80-a-barrel range, Buffett's still a net seller of oil stocks.

Putting it all together
So here's where Mr. Buffett's trading activity has me puzzled: What, I ask you, is the key reason for buying railroad stocks?

I submit to you that you buy a railroad for one of two reasons: Either (a) you believe the U.S. economy is ready to rebound, that the need to move goods from place to place will increase, and that this will benefit the railroads, or (b) you believe that the economy is ready to rebound, driving oil higher and increasing the relative competitiveness and efficiency of rail, or (c) both.

Yet here we see Buffett buying a big railroad at the same time as he sells two of the biggest names in Big Oil.

What in the world is Warren Buffett thinking?
And this is what has me flummoxed. It's been nearly six months now since Warren Buffett told investors that the recession was over, that the economy had "sort of plateaued at the bottom," and was bound to rise again. But while his lips say "yes," the stocks Buffett's eyeing seem to say "no, I'm not convinced it's really over yet." Now Buffett has explained his sales of Conoco as a move to harvest tax losses, but is that all his sales amount to?

Do you see method in Warren Buffett's apparent investment madness? If so, we're all ears. Scroll down, and post your thoughts below.

Berkshire Hathaway, CarMax, WellPoint, and Wal-Mart are Motley Fool Inside Value recommendations. Berkshire Hathaway is a Stock Advisor selection. Procter & Gamble and Republic Services are Income Investor choices. The Fool owns shares of Berkshire Hathaway and Procter & Gamble.

Fool contributor Rich Smith does not own shares of any company named above. The Fool has a disclosure policy.