AAR said 110,164 carloads of crude oil were shipped during the first quarter of the year.
"[That's] 1.4 percent more than in the fourth quarter of 2013 and, by 1,559 carloads, the most ever in any quarter," the association said in a statement Thursday. "In the first quarter of 2014, crude oil accounted for 1.6 percent of total originated carloads for U.S. rail traffic."
The U.S. Energy Information Administration, the statistical arm of the Energy Department, said in its latest monthly report total U.S. crude oil production averaged 8.3 million barrels per day in April, the highest monthly average since March 1988. By 2015, the average should reach 9.2 million bpd, the highest level in more than 40 years.
The increase in crude oil production is more than the existing pipeline infrastructure in the United States can handle, industry officials say. That means energy companies are using rail as an alternate shipping method.
The increase in oil sent by rail has raised safety concerns following a string of derailments involving trains carrying crude oil. A wreck in Lac-Megantic, Quebec, last year left more than 40 people dead.
U.S. Transportation Secretary Anthony Foxx in May said "all options are on the table" when it comes to ensuring oil transport by rail is safe.