ConocoPhillips, the third-largest U.S. oil producer, yesterday posted the highest quarterly profit in its history after crude prices climbed to a record and natural gas surged to a 2 1/2 -year high.

Second-quarter net income jumped 18-fold to $5.44 billion, or $3.50 a share, from $301 million, or 18 cents, a year earlier, the Houston-based company said in a statement.

U.S. oil futures rose above $140 a barrel for the first time in June and natural gas rose even faster in this year’s first half. Price gains made up for a drop in output and the inability of ConocoPhillips, the number-two U.S. maker of gasoline and diesel, to pass on the full brunt of record crude costs to motorists.

“These are blowout results,” said Robbert Van Batenburg, head of research at Louis Capital Markets in New York. “It’s tough to argue with that, and it’s a direct function of the high oil prices, which also eat away at some of the margins on the refining side.”

ConocoPhillips said second-quarter revenue jumped 51 percent to $71.4 billion. Even excluding $4.51 billion in costs last year related to an asset seizure in Venezuela, earnings from oil and gas sales surged 90 percent to $4 billion.

ConocoPhillips is first among the major U.S. oil producers to report earnings for the quarter. The biggest, Exxon Mobil Corp., is scheduled to release its results on July 31, and Chevron Corp. reports the following day.

ConocoPhillips fell $2.48, or 2.9 percent, to $81.83 in New York Stock Exchange composite trading, dropping along with oil futures. The stock climbed 24 percent in the second quarter, the biggest gain among the four largest U.S. oil companies.

Higher-than-expected profit from the company’s 20 percent stake in Russia’s OAO Lukoil helped ConocoPhillips exceed earnings estimates, J.P. Morgan analyst Michael LaMotte said. Profit from the stake rose 47 percent to an estimated $774 million, ConocoPhillips said.

Energy companies are struggling to increase production as oil-rich governments limit access to the world’s largest fields and competition increases from producers in countries such as India and China. As oil prices rise, many production-sharing contracts transfer increasing volumes of output to the host governments.

ConocoPhillips Chief Executive Officer Jim Mulva has sought to counter limitations overseas by investing more in developed countries, where contracts are more readily enforced and producers pay royalties, rather than sharing production with governments.

Production will increase in the fourth quarter, allowing ConocoPhillips to meet its full-year output target of 1.8 million barrels of oil equivalent a day, Mulva told investors on a conference call.

Increased oil and gas earnings offset a refining business weakened as crude prices rose faster than gasoline and diesel. The 90-percent increase in the second-quarter average for oil futures prices was more than double that of gasoline futures.

ConocoPhillips said its earnings from refining fuels fell 72 percent from a year earlier to $664 million. Margins surged in 2007 as price gains at the pump outpaced crude’s rise.

“A year ago, refining and marketing was golden,” said Bernard Picchi, an analyst at Wall Street Access in New York. “Everything worked perfectly.”

ConocoPhillips ranks behind only San Antonio-based Valero Energy Corp. in U.S. oil-processing capacity. The company got almost half of its profit from refining last year.