HOUSTON — Oil giant Exxon Mobil Corp. topped its own record for the biggest annual profit by a U.S. company last year, racking up earnings that amounted to $4.5 million an hour for the world's largest publicly traded oil company.

It reported the record net income — $39.5 billion — despite a 4 percent drop in earnings in the final three months of 2006, as prices for oil and natural gas fell from extraordinary levels earlier in the year.

Lower commodity prices may linger for at least the first part of 2007, even as the cost of doing business rises because of factors such as a shortage of drilling equipment and labor.

So while big players like Exxon Mobil Corp., Chevron Corp. and ConocoPhillips — first, second and third, respectively, among integrated U.S. oil companies — are expected to continue to rake in piles of cash, the totals aren't likely to be the eye-popping amounts of recent quarters.

"I'd say overall, if you look for earnings to decline 5 to 15 percent from the huge highs this past year, you're probably going to see most of these companies fall within that range," said John Parry, a senior analyst at energy consulting firm John S. Herold Inc.

ExxonMobil's profits didn't go unnoticed on Capitol Hill, where one lawmaker called them "outlandish" and said oil companies have benefited too long from a Republican-backed energy policy that cheats American taxpayers.

ExxonMobil wasn't alone among oil and gas entities posting a huge profit in 2006. On Thursday alone, three other companies — Royal Dutch Shell PLC, Marathon Oil Corp. and Valero Energy Corp. — also reported best-ever full-year profits. The four companies combined had earnings of $75.6 billion last year.

Last week, Houston-based ConocoPhillips said its $15.5 billion profit last year topped its previous record from 2005 by about $2 billion dollars.

Chevron is scheduled to report 2006 results Friday.

ExxonMobil's 2006 profit beat its own previous record for a U.S. company of $36.13 billion set in 2005. Its net income for 2006 equals the approximate gross domestic product — a measure of all goods and services produced within a country in a given year — of countries like Ecuador, Luxembourg and Croatia.

Also notable was ExxonMobil's revenue, which rose to $377.64 billion for the year, surpassing the record $370.68 billion it posted in 2005.

"ExxonMobil continued to leverage its globally diverse resource base to bring additional crude oil and natural gas to market," said Rex W. Tillerson, chairman of the Irving, Texas-based company.

ExxonMobil's record earnings followed a year of extraordinarily high energy prices as crude oil topped $78 a barrel in the summer — driving up average gasoline prices in the United States to more than $3 a gallon. Prices retreated later in the year as crude oil supplies grew and concerns over Middle East tensions eased, among other factors.

The fourth-quarter decline reflects lower profits from ExxonMobil's refining and marketing operations and a sharp drop-off in natural gas prices.

The results for the October-December period mimicked those of ConocoPhillips, which last week said its fourth-quarter profit fell 13 percent — also primarily because of lower natural gas prices and refining margins. Analysts largely have predicted declines in fourth-quarter earnings for the big U.S. oil companies because of the moderation in commodity prices.

Still, not everyone's applauding Big Oil's big profits. U.S. Rep. Edward J. Markey, D-Mass., a member of the House Energy and Commerce and Natural Resources committees, said the Bush administration and the recent GOP-controlled Congress consistently "stuffed energy bills full of goodies" that benefit oil companies at the expense of taxpayers.

ExxonMobil's record profit is "the direct result of a Bush energy policy that for seven years has used every lever of the American government to tilt the scales toward satisfying the special interest demands of a single industry at the expense of the public interest," said Markey.

Ken Cohen, ExxonMobil's vice president for public affairs, said the company's profits are the result of billions in capital investment over long periods in a volatile industry. He also noted the company's U.S. tax obligation in the past five years was about $60 billion — about $20 billion more than its U.S. net income for the same period.

"When we make more money in our industry, the government gets significantly more money," Cohen said.

While ExxonMobil's earnings seemed to draw some flak in Washington, Wall Street appeared pleased. The company's shares gained 98 cents, or 1.3 percent, to close at $75.08 on the New York Stock Exchange.