Tropical Storm Harvey is tearing through one of the nation's most important energy hubs. Throughout the Gulf Coast, key refineries and production facilities have been forced to close.

Rain and flooding are continuing to wreak havoc on Houston and the surrounding area, and the rain is forecast to continue through the week. The devastating storm's full impact on the region's oil and gas infrastructure won't be known until coming days.

Ten oil refinery plants in the Houston area and Corpus Christi are shutting down because of the storm, according to a report released Sunday by S&P Global Platts. They normally have the capacity to refine about 2 million barrels of oil a day.

That included Exxon Mobil (XOM)'s Baytown refinery, the second largest in the country. The campus, about 25 miles east of Houston, can process up to 584,000 barrels of crude oil per day. It employs about 7,000 people.

Related: Gas prices set to spike as Harvey pummels Houston

S&P estimated Sunday that roughly 2.2 million barrels per day of refining capacity were forced offline because of the storm.

Overall, the Gulf area is home to refineries and other operations that account for nearly one-third of the nation's capacity to turn oil into gas, diesel and other products.

Harvey's market impact became clear Sunday night when U.S. gasoline futures spiked 7% after energy markets reopened.

One factor that could lessen the impact of Harvey's damage: The world has a glut of oil.

"As more refineries go offline, there's less stress to the system because it's well supplied," said Rob Smith, a director at IHS Markit.

Live updates from CNN on Harvey and its toll

Harvey made landfall as a Category 4 hurricane late Friday, but was downgraded to a tropical storm by mid-Saturday. It continued to dump huge amounts of rain on Houston and cause dangerous flooding that could get worse.

Federal officials said Sunday that workers from 105 oil and gas production platforms had been evacuated. All told, 737 platforms in the Gulf are staffed with workers.

About 22% of the oil produced in the Gulf was shut down as of Sunday, according to the Interior Department's Bureau of Safety and Environmental Enforcement. That amounts to nearly 379,000 barrels of oil per day.

The numbers were a slight improvement over Saturday, when about a quarter of oil production in the Gulf was closed.

The bureau also estimated Sunday that about 26% of natural gas production in the Gulf has been shut.

Related: Harvey could hit the Texas economy

Harvey is the first major storm to seriously threaten the Gulf Coast energy sector in a while.

Hurricanes Gustav and Ike in 2008, as well as Hurricane Isaac in 2012, all knocked more than 1 million barrels of Gulf oil production offline, according to the EIA. Those hurricanes also temporarily disrupted refining capacity.

Hurricanes that land in Texas tend to have little impact on oil production, but more significant consequences for refining, according to Tom Kloza, chief oil analyst at the Oil Price Information Service.

While refineries in Corpus Christi were already closed ahead of the storm, flooding in the Houston area forced more closures Sunday.

By late afternoon, plants run by Exxon, Citgo, Petrobras, Flint Hills, Magellan, Buckeye, Shell, Phillips 66 and Valero Energy (VLO) had all closed because of the storm, according to S&P Global Platts and the companies.

Valero reported Sunday that there were no "substantial refinery impacts" because of the storm. The company said it is working with government officials to figure out what it needs to do to resume operations.

The company's Corpus Christi plant produces 293,000 barrels per day, while its Three Rivers plant produces 89,000 barrels.

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Houston also marks the beginning of the Colonial Pipeline, which transports more than 100 million gallons of gasoline, heating oil and aviation fuel each day to as far as the New York harbor. Power outages during Hurricanes Katrina and Rita in 2005 forced the shutdown of parts of the Colonial Pipeline for several days.

Kloza said that normally refining is knocked offline for just a brief time, making the impact on prices fleeting. But that depends on the severity of the storm.

"Katrina was the exception," Kloza said, referring to the 2005 storm that badly damaged Gulf Coast operations.

He predicted on Thursday that Harvey is likely to cause only a short-term jump in gas prices of 5 to 10 cents per gallon, though he said a 25-cent spike in a worst-case scenario was also possible.

The average price of a gallon of regular gasoline nationwide has ticked up a few cents in recent days, according to AAA.

"You're talking about a situation where a month from now gas prices will probably be lower. But a week from now they'll be higher," said Kloza.

--CNNMoney's Nathaniel Meyersohn and Kaya Yurieff contributed to this story.