After sitting on top of the Fortune 500 list last year, Exxon Mobil (NYSE: XOM) gave the top slot back to perennial leader Wal-Mart (NYSE: WMT) this year. This marks that fifth time in six year that Wal-Mart has occupied the pole position.

It was definitely a close battle for the top position and Exxon Mobil did not get beat by too big of a margin. For the full year 2006, Exxon Mobil saw revenues of $347.2 billion which was just a bit shy of Wal-Mart's $351.1 billion. While the battle for the #1 spot was a close one, there was really no other competition for Exxon and Wal-Mart with the #3 company coming in well beneath the big 2. Earning #3 on the list this year was General Motors Corp. (NYSE: GM) with $207.3 billion in revenue. Granted the biggest difference is that GM actually lost money last year despite the large revenues it was able to pull in.

The remaining two slots in the top 5 also went to oil companies with Chevron Corp. (NYSE: CVX) pulling in the #3 slot with $200.5 billion in revenues and ConocoPhillips (NYSE: COP) rounding out the #5 slot with a respectable $172.4 billion in revenues for the year.

Last year was definitely a good year to be in the oil business, and it is definitely shaping up to be another stellar year. It's hard to bet against oil these days!

If you are interested in seeing where your favorite companies ranked, you can find a full list of the top 500 companies here.

Michael Fowlkes has worked as a stock trader for seven years and spent the last two years working as an analyst for the online investment advisory service Investor's Observer. DISCLOSURE: Mr. Fowlkes owns and/or controls diversified portfolios of long and short stock and option positions that include holdings in XOM.