About 10.3 million barrels of petroleum and petroleum products traveled the U.S. rail system last week, the Association of American Railroads said.

AAR released its rail traffic report for the week ending March 22. It said 14,811 railcars, or about 10.3 million barrels barrels of petroleum and petroleum products, were delivered last week, a 10.3 percent increase year-on-year.

Last week's total was 3.1 percent higher than for the week ending March 15.

The rail group said Thursday that so far this year, 120 million barrels of petroleum and petroleum products were delivered by rail in the United States, a 6.9 percent increase from the same period in 2013.

Industry officials said the increase in oil production from shale deposits in the U.S. has strained existing pipeline capacity, forcing some energy companies to turn to rail as an alternative transit method.

The U.S. Energy Information Administration said in its March market report U.S. crude oil production should reach 8.4 million barrels per day by the end of 2014, a 12 percent increase from the previous year.

The AAR's rail count excludes deliveries from the Canadian National Railway Co. and Canadian Pacific Railway.