The Dow Jones industrial average was off more than 165 points at midday Monday, or 0.61 percent, amid concerns the weekend attack on two Saudi oil installations would keep crude prices elevated long term. But the prospect of tightening supplies sent energy stocks higher.

Shares in the big international oil companies — known as the supermajors — climbed on global markets. U.S. petroleum giant ExxonMobil advanced more than 1.5 percent, to $73.74; Chevron was up nearly 2 percent, to $123.87; while BP spiked 3.2 percent, to $39.09. Companies that service and supply the supermajors and Middle East producers were up even more. Schlumberger Limited jumped 5 percent and Halliburton leaped 6.6 percent on expectations of more business following the attacks.

“The Schlumbergers and the Halliburtons supply the equipment for the drilling, so if we have a big supply disruption like we have now, they are going to have to do the drilling and probably the repairs,” said Bill Selesky of Argus Research. “That’s why those two are both trading up pretty good today.”

On Sunday, President Trump said via Twitter that he had authorized the release of oil from the Strategic Petroleum Reserve to ensure against supply disruptions. He also said U.S. agencies have been directed “to expedite approvals of the oil pipelines currently in the permitting process in Texas and various other States.”

The attack on Saudi Arabia’s oil infrastructure immediately knocked out 5.7 million barrels — or nearly 6 percent of the 100 million barrels the world consumes per day. It was unclear Monday how long it would take for the Saudis to restore full production.

“A supply disruption on this scale is an extraordinary event,” said Pavel Molchanov, an oil analyst with Raymond James. “No single disruption on this scale has occurred in decades.”

U.S. oil prices have been trading in a belt between $50 and $60 a barrel in the past six months. Brent crude, the global benchmark, has been trading slightly above that range. Most oil companies and nations favor world oil prices in the $70 to $80 range, which allows a healthy profit without rattling the economy or sparking a rush for petroleum alternatives.

The weekend attack took out a Saudi Aramco oil processing plant and nearby oil field. The state-run company is the second-largest oil producer in the world at 9.85 million barrels per day in August. Aramco is reportedly considering a delay in its initial public offering until production returns to normal.

“I don’t think even Aramco’s limited listing on the Saudi stock exchange can withstand this event,” said John Kilduff of Again Capital. “This attack is a material adverse change to the company. They are going to have to do a lot more risk disclosure in their IPO document as it relates to Iran and the region.”

A jump in oil prices is likely to weigh on an already-declining global economy, one beset by the U.S. trade war with China, White House sanctions against Iran and a decade-long economic expansion that shows signs of petering out.

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American consumers, who have been powering the current economic boom, would get hurt if the price spike settles at the gasoline pump for an extended period of time.

“Oil price spikes due to geopolitical crises in the past have had a depressing impact on U.S. consumers when they filled up their tanks,” said Ed Yardeni, president of Yardeni Research. “It costs them a few more bucks when they fill up, and so consumers hunker down and cut spending in other areas. That hurts the economy.”

On Sunday, Saudi officials said only one-third of the affected 5.7 million barrels would be restored by Monday, leaving millions of barrels per day offline indefinitely.

With oil giants Venezuela and Iran mostly absent from world markets, an extended Saudi supply disruption could force industrial economies such as the United States to tap emergency reserves. There are 1.5 billion barrels available in strategic reserves among industrial economies. Saudi Arabia also stores oil in strategic, overseas locations in Europe and Asia.

“There’s a lot of oil out there in reserve,” said U.S. Energy Secretary Rick Perry in an interview Monday with CNBC.

The U.S. Strategic Petroleum Reserve currently holds 645 million barrels, equal to about one month of U.S. oil consumption.

“The good news is that there is more than enough oil in inventory to prevent fuel shortages,” Molchanov said. “There are not going to be gasoline lines like there were in the 1970s.”

Yemen’s Houthi rebels asserted responsibility for the weekend blasts, but the United States blames Iran for the “unprecedented attack on the world’s energy supply.”

Tehran has denied responsibility.

The last time the world lost a comparable slice of its oil supply was during the Gulf War. There was a substantial increase in global oil prices, but the process was gradual because the war had been expected.

Oil prices result from a careful balance of supply and demand. Supplies have been mostly in balance this year, with U.S. production making up for declines in Venezuela and Iran.

Even though the United States produces more oil than ever before — close to 12 million barrels a day — a disruption halfway around the world can send prices soaring on global markets.

But Americans are more insulated from dramatic swings because technological advances have increased domestic oil output and heightened efficiency, from automobile mileage to home heating. U.S. shale oil production has reduced domestic demand for oil from the Persian Gulf from 3 million barrels a day in 2003 to 1 million barrels. The U.S. economy is much less dependent on manufacturing than it was during the oil price spikes of the 1970s and ’80s.

Oil companies are also a smaller piece of the stock market. The energy sector made up more than 20 percent of the total value of Standard & Poor’s 500-stock index in the 1970s. Now it’s only 4.44 percent.

Oil prices have been relatively calm in recent weeks because of high production and slowing demand. But trade disputes, sanctions against Iran and Venezuela’s internal meltdown have contributed to confusion in oil markets.

U.S. oil production has helped keep a lid on gasoline prices. Americans this month saw the lowest Labor Day gas prices in three years.

Saudi Arabia has been the industry’s great stabilizer, with $10 trillion worth of oil under its sands. But the kingdom and other members of the Organization of the Petroleum Exporting Countries have been unable to limit production enough to keep prices within the sweet spot of $70 to $80 a barrel.