The deadly explosion of oil tank cars in Quebec highlights the risk of moving oil by train as the volume of crude shipped via U.S. rail lines continues to climb.

The amount of U.S. crude oil traveling by rail has increased 23-fold — from 9,500 cars in 2008 to more than 233,000 last year — as drillers extract more oil than existing pipelines can carry. In North Dakota, three-fourths of the state’s crude was shipped by railroad in April, and much of it passed through the Twin Cities.

Canadian investigators are trying to determine what caused a parked train with 72 tank cars to begin rolling and then derail early Saturday morning, triggering fires and explosions in Lac-Mégantic, Quebec, that killed at least 13 people. Many others are still missing.

The tank cars were loaded with oil in New Town, N.D., by Wayzata-based rail carrier Dakota Plains Holdings, and were destined for a refinery in New Brunswick, according to World Fuel Services Corp., the shipper’s parent company.

The train’s exact route eastward was not immediately known, including whether it passed through the Twin Cities, a waypoint for Canadian Pacific and the BNSF, two of the nation’s largest railroads. A lack of information on day-to-day train movements makes it difficult to assess possible problems and prepare accordingly, said Rick Larkin, director of emergency management for St. Paul. “We thrive on information to be able to understand the risk,” Larkin said. “We need that data in order to develop plans and a risk profile.”

Other emergency officials also said they don’t have daily reports on hazardous materials on trains, although the railroads share information regularly. That information is not available to the public, a state official said. But railroads are known to be sending many crude-only “unit trains” — like the one in the Quebec accident — through Minnesota.

Transporting crude oil by rail was a rarity six years ago because it wasn’t considered a cost-effective option to pipelines. But the surge in domestic oil production has exceeded pipeline capacity, while higher crude prices have made shipping by rail, at times, a profitable alternative. Rail lines also can reach many refineries not served by pipelines.

The industry’s growth continued in the first quarter with a record 97,135 tank cars of crude oil shipped, up 20 percent from the prior quarter and 166 percent higher than a year earlier, according to the American Association of Railroads. The trade group contends that shipping oil by train is as safe or safer than pipelines.

Larry Mann, a New York attorney who wrote a book on railroad safety, said the early reports about the Lac-Mégantic catastrophe raise questions about whether manual brakes had been set on the unattended train operated by the Montreal, Maine & Atlantic Railway.

“Apparently these cars were sitting there a long time and the brakes were not applied,” he said in an interview.

The railroad did not return phone calls seeking comment.

Much of the rail industry remained silent Monday. Canadian Pacific, whose U.S. headquarters is in Minneapolis, said it had no comment out of respect for the Lac-Mégantic victims. Dakota Plains officials did not return phone calls, and directed them to the shipper and venture partner, World Fuel Services, which said it “is deeply concerned for all those impacted by loss of life and destruction caused by the tragic accident.”

Mann said the accident shows a need for stronger crude oil tank cars with double walls and features like those required on cars that carry liquefied natural gas and other hazardous materials. “They need to retrofit the existing fleet and put the safety features on all the new ones,” he said.

Patti Reilly, a spokeswoman for the railroad trade group, said the industry imposed more stringent standards on rail cars in 2011 even though it was not required by federal regulations. The standards include thicker walls, but not double walls.

Pipelines, which some experts consider safer than rail for transporting crude, have provoked concerted opposition on safety and environmental grounds, especially the Keystone XL project, which would deliver Canadian oil through western states. Rail transportation of crude hasn’t faced similar organized opposition.

Minneapolis Fire Chief John Fruetel said railroads have not experienced major crude oil disasters. Most accidents, like one in Parkers Prairie, Minn., in March, involved spillage of crude oil, but no injuries.

Both Minneapolis and St. Paul, as well as the state, have hazmat teams on duty at all times. Fruetel said the teams typically don’t focus on one hazard, such as crude oil, and instead focus on responding to any kind of disaster. “We’ve always had major rail going through the city and different types of mixed loads,” he added.

But recently, Minneapolis emergency responders received training that included specific responses actions in crude oil disasters, Fruetel said. State responders have received similar training. Sandy Fielden, an analyst for RBN Energy of Houston who has closely tracked the crude-by-rail industry, said it’s too early to say what effect the Quebec catastrophe will have on the future of moving oil by rail.

“People are going to wait to find out a little bit more about exactly what happened,” he said.