Exxon has once again surpassed Apple as the world's most valuable company after the iPhone and iPad maker saw its stock price falter.

Apple Inc.'s stock has been on the decline since the company's quarterly earnings report Wednesday suggested that its fast growth phase, rare for a company of its size, may be coming to an end.

Apple's stock fell 2.4 per cent to close Friday at $439.88 for a market capitalization of $413 billion. That followed a 12 per cent drop on Thursday, the biggest one-day percentage drop for the company since 2008.

Exxon Mobil Corp. gained 38 cents Friday to $91.73 for a market capitalization of $418 billion.

Apple first surpassed Exxon in the summer of 2011, displacing the oil company from a perch it had held since 2005. The two companies traded places through that fall, until Apple surpassed Exxon for good in early 2012 at least until Friday.

China's largest oil company, PetroChina, could lay claim to having hit a market capitalization even higher than either Exxon's or Apple's, but only based on prices on the Shanghai stock exchange, which is isolated from the rest of the financial world because of Chinese laws on foreign investment. PetroChina's shares also trade in Hong Kong and on the New York Stock Exchange. Based on prices there, its market capitalization never went as high as $500 billion.

Apple and Exxon are among only a half dozen U.S. companies to have ever reached $500 billion in market value. Apple and Microsoft Corp. are the only ones to have ever hit $600 billion.

AP