Apple becomes world's largest company once again. Sorry, Exxon.

Apple surged past Exxon Mobil as the world's biggest company—and many investors believe it's still cheap.

Apple reported earnings on Tuesday that blew past analysts’ expectations as the tech juggernaut sold an astounding 37 million iPhones during the last quarter.

At its intraday high price Wednesday, Apple’s market value reached $423.7 billion, up eight percent from $391.9 billion a day earlier.

That pushed it past Exxon Mobil’s market capitalization, which was $416.5 billion at its high during the session.

Apple has “$98 billion in cash, 116 percent EPS growth, and a depressed valuation,” wrote Goldman Sachs analyst Bill Shope, who raised his 12-month forecast on the shares to $600 from $550. “Our target price continues to be based on a 15 multiple on our revised 2012 EPS estimate.”

Along with sporting a quite reasonable price-earnings ratio, analysts and investors also expect Apple to declare a dividend for the first time this year, making the shares even more attractive.

After Apple and Exxon, there is a big drop off in size for the biggest publicly-traded companies in the world.

Beijing-based PetroChina comes in third at about $270 billion, followed by Microsoft, worth $245 billion.

Fourth-quarter iPhone shipments topped even the highest estimate on Wall Street: a 33 million estimate from Jefferies. iPad, Mac, iPod sales all exceeded consensus analysts’ expectations, along with the company’s gross margin, coming in at almost 45 percent.

“The company trades at 11 times this year earnings, which are expected to grow more than 40 percent,” said Paul Hickey of Bespoke Investment Group. “It’s certainly hard to take the other side of the argument.”

Apple surpassed Exxon in market value briefly last August, only to fall back  as investors worried about the future of the company in the wake of Steve Jobs’ death. Others simply sold the stock to raise funds amid a breakout in the European credit crisis.

It could come down to the wire today as to whether Apple can hold the top spot. As of this writing, Apple’s market value stood at $417 billion, compared to $413 billion for Exxon.

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