SAN FRANCISCO (MarketWatch) -- A production slowdown at the nation's refineries, now operating at levels last seen in the aftermath of Hurricane Katrina in 2005, couldn't come at a more troublesome time for consumers watching pump prices flirt with $4 a gallon.

Such low production rates could create a new set of problems for refiners, already operating at the brink of loss. Utilization rates at 30-month lows threaten to spark probes by lawmakers, who have been holding a series of hearings on the rampant rise in gasoline and diesel prices.

"If this operating level persists, the industry will likely see another round of intense legislative scrutiny," said John Kilduff, an analyst at futures brokerage MF Global.

U.S. refineries operated at 81.4% of their operable capacity in the week ending April 11, the Energy Department's statistical arm said last week. The last time the utilization rate fell below 80% was in October 2005 after hurricanes Rita and Katrina devastated refineries along the U.S. Gulf Coast.

The culprit is a record run in oil prices, which are rising much faster than gasoline prices. Near-term crude futures, which hit a new record above $117 a barrel Monday, have accelerated 80% in the last 12 months. Gasoline futures and retail prices also keep hitting new records. But the yearly gain of 41% in gas futures has not been nearly as dramatic. See more on oil and gas futures.

The gap between the price of crude and the price of gasoline and other refined products has pressured profit margins at refiners Valero Corp. VLO, -3.14% , Tesoro Corp. TSO, and Sunoco Inc. SUN, +0.64% , among others.

Earnings from downstream operations including refining slumped 62% for a group of 10 major U.S. oil companies in the fourth quarter. At the same time, these companies processed roughly the same volume of oil, says the Energy Department's Energy Information Administration.

“ 'This is a maintenance season. If you can't make a lot of money, you do a little more repairs.' ” — James Williams, WTRG Economics

The first quarter is likely to look even worse. Earnings for the three dedicated refiners in the S&P 500 Index SPX, -0.48% are anticipated to tumble 94% to just under $67 million from $1.2 billion a year ago, according to Thomson Financial.

A good time for maintenance

With higher costs cutting into their bottom line, refiners appear to have decided that this spring is a particularly opportune time to take more of their production offline and retool their plants.

"This is a maintenance season. If you can't make a lot of money, you do a little more repairs," said James Williams, an economist at WTRG Economics, an energy-research firm.

Spring is typically when refiners idle parts of their plants to undertake maintenance. But they don't always cut back so drastically. Last April, when the difference between crude and gasoline prices was narrower, the utilization rate touched 90%. The nation's refinery-utilization rate has remained under 90% since early January.

Still, analysts anticipate this production rate could pick up again if gasoline-price growth accelerates ahead of the key summer-driving season.

"I expect the rate to go up dramatically, probably passing 90% in a month," Williams added.

Already this year, the gap between crude prices and gasoline has narrowed. Near-term crude futures have risen 22% this year, while gasoline prices have gained 20%.

The EIA said last week that gasoline could surpass $4 a gallon in the upcoming driving season in some areas. Retail regular-gas prices averaged $3.503 a gallon on Monday, a new record high, according to AAA.

Crunch time for refiners

That improvement won't help companies with big refining operations in the upcoming quarterly earnings season.

Chevron Corp. CVX, -2.74% , the nation's second-largest energy company, said earlier this month that its refining operations have been hurt by weak profit margins, although total earnings will likely get a big boost from record-high oil and natural-gas prices. The company's downstream segment made up about one-fifth of its total earnings last year.

Valero Energy VLO, -3.14% , the United States' largest refiner, warned last month that sharply lower margins from refining crude means first-quarter profit margins will be "significantly lower" than in the year-ago quarter.

Nonetheless, companies such as Exxon Mobil Corp. XOM, -2.91% , which makes a big chunk of its profit from oil production, are still expected to report record earnings. Exxon Mobil last year posted the largest annual profit by a U.S. company -- $40.6 billion.

At the same time, Congress continues to prod the oil industry for explanations on high gasoline and diesel prices. On Thursday, a House panel on energy independence and global warming will hold a hearing on "gas prices and the Strategic Petroleum Reserve."

Earlier this month, thousands of independent truckers protested high diesel prices as House lawmakers grilled top oil-company executives on tax breaks.

National average diesel prices touched a new high of $4.20 a gallon on Monday, AAA said. National gasoline prices reached a new record of $3.503 a gallon, though they have been topping $4 in some parts of the country.