For several years, Exxon Mobil has been the world's most valuable company on the stock market. But now Apple, the U.S. consumer technology company, is contesting the oil giant's claim to the top spot.

On Tuesday, for a few hours, Apple was No. 1. The stock market value for Apple, the maker of the popular iPhones, IPads and Mac computers, surpassed that of the U.S.-based Exxon. But by the end of the day, the oil company had regained the lead.

Financial analysts say the values of the two companies are likely to continue to fluctuate, perhaps more so for Exxon, as the worth of its oil holdings continues to rise and fall on world markets. After the U.S. central bank, the Federal Reserve, decided Tuesday to keep its benchmark interest rate at a historically low level for the next two years, oil prices edged higher again and continued upward on Wednesday. That boosted Exxon's fortunes.

Apple's march to near the top has been fraught with corporate missteps followed by marked success. In the 1990s, it was a relatively minor player in the technology industry and flirted with bankruptcy. But Apple transformed itself from a personal computer manufacturer into a company producing the trendy iPhone and the iPad tablet for audio-visual media.

As trading ended Wednesday, Exxon was valued at nearly $353 billion and Apple at nearly $347 billion.