On Thursday the whiff of $40 oil helped Exxon shares reach a two-year high of $44.24, giving the company a market value of $287 billion.

GE, which makes everything from light bulbs, mortgages and sitcoms to jet engines and power-plant turbines, still has a comfortable lead at $311 billion, about 8 percent higher. But analysts say its place at the top is in jeopardy.

"You don't need that much of a jump (by Exxon) for this to happen," Standard & Poor's equities analyst Howard Silverblatt said. "Oil prices are going up, while GE has a lot of financing businesses, where rising rates can interfere with earnings."

GE disputes the idea that higher rates will have a major impact on its results.

S&P, the credit rating agency that manages the benchmark S&P 500 Index, forecasts Exxon's market value will reach $328 billion this year -- though it will be a photo finish with software giant Microsoft Corp. (Nasdaq:MSFT - news)

GE, meanwhile, could slip to $306 billion, according to S&P forecasts, as its earnings power dims this year. If the lead does change hands, it would cap off a remarkable period for the energy sector.

GE was the most valuable U.S. company on Dec. 31 for the better part of 10 years, with the exception of 2002, 1999 and 1998, when New Economy fervor propelled Microsoft to the top spot.

GE was also among the five largest U.S. companies throughout the 1980s and early '90s.

To be sure, these figures are only snapshots in time. Predecessor company Exxon Corp. ranked atop the S&P 500 at the end of 1990 through 1992, when military action in Iraq (news - web sites) last sent oil prices above $40 a barrel.

"While market cap is certainly one indicator of success, we are prouder of the disciplined management that we bring," said Exxon Mobil spokesman Tom Cirigliano.

ENERGY SURGE

It's no secret that Exxon's fortunes rise and fall with the price of energy commodities. And with oil and gas profits gushing, investors have sent Exxon shares up 25 percent in the past 12 months, outperforming the S&P 500 by three points.

But those profit swings are the main reason oil stocks are less valuable. Exxon shares currently have a price-to-earnings multiple of 17, a steep discount to the S&P 500's multiple of about 27 times earnings.

Shares of GE, a diversified industrial and financial conglomerate, fetches 20 times earnings.

Still, a growing number of investors have concluded energy prices won't fall back to historic averages any time soon.

On Friday oil broke through the $40 a barrel mark, the highest level since Iraq invaded Kuwait in October 1990, on worries about security concerns in the Middle East and thin U.S. gasoline supplies. Oil closed at $39.93 a barrel, up 56 cents.

High energy prices are bad news for the global economy, but they've generated windfall profits for Exxon. In the first quarter, the Irving, Texas, company reported record earnings of $5 billion, putting it on track to surpass last year's record profit of $21.5 billion.

"Unless oil and gas collapse I think Exxon Mobil could earn $22 billion to $23 billion this year," said analyst Fadel Gheit of Oppenheimer & Co.

And while energy shares have soared, GE shares have slipped 2.3 percent this year and more than 10 percent since reaching a two-year high in late January. GE's net income in the most recent quarter was $3.24 billion.