Apple is poised to surpass Exxon Mobil as the most valuable company in the world.

NEW YORK (TheStreet) -- Apple's(NYSE:AAPL) iPhone is now more important than crude oil. At least, with Apple's after-hours rally on a blowout quarter about to send its market cap to $420 billion, it will surpass Exxon Mobil(NYSE:XOM) as the most valuable company in the world.

Market capitalization may not be the best valuation tool for investors -- last year, there were times when Exxon Mobil, Apple and Warren Buffett's Berkshire Hathaway(NYSE:BRK.B) were all jockeying for top position among the top three places on the market-cap list. Berkshire is now less than half the market cap of Apple and Exxon Mobil, though it was a two-horse race most of the time, and now the race has definitively left Buffett with lots of ground to make up.

Ask the iPhone's Siri "What is the biggest market cap company in the world?" and it will give you a new answer starting Jan. 25

There are other ways to size up the mega-cap competition, too. When it comes to revenue, Apple still can't hold a candle to Exxon Mobil: Apple may have blown past all estimates with $46 billion in revenue, but for Exxon Mobil, $46 billion would be a global economic disaster quarter. The Wall Street consensus for Exxon Mobil revenue in the fourth quarter is $119 billion. Exxon Mobil's quarterly profit line alone often surpasses the GDP of many small countries -- last quarter it rivaled the GDP of Malta and surpassed the GDP of the Bahamas.

That said, Apple just earned $13.87 a share, vs. an expectation for just under $2 from Exxon Mobil in quarterly earnings -- to be reported next week. And with an iPhone costing $199 with a two-year contract and a barrel of oil hovering around the $100 mark, the most precious commodity in the world isn't just reflected in the new king of market cap.

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