Crude oil exported from Canada by rail topped 140,000 barrels per day during fourth quarter 2013, nearly double the 2012 figures, a regulator said.

The National Energy Board, Canada's energy regulator, published quarterly data for crude oil exports by rail Monday. It said that, combined, 184,907 barrels of oil per day were delivered by rail over 2012, with more than 40 percent of that volume sent during the fourth quarter.

Fourth quarter 2012 exports by rail were 79,763 bpd, compared with the 146,047 bpd sent during fourth quarter 2013. Overall 2013 deliveries by rail were 502,215 bpd.

An accelerated rate of crude oil production in North America has strained existing pipeline capacity. Industry officials say rail transport is taking up the slack.

Increased crude oil deliveries by rail corresponded with an increase in derailments. More than 40 people were killed last year in Lac-Megantic, Quebec, when a train carrying crude oil derailed and caught fire.

Canadian Transport Minister Lisa Raitt announced new regulations last month aimed at increasing safety on the Canadian rail system. The measure from regulator Transport Canada started with an order to remove around 5,000 tanker cars designated DOT-111 from service almost immediately.