Enbridge Inc, Canada's No. 2 pipeline company, said on Monday faster than expected growth in North American oil output means its lines could be at full capacity as soon as 2016 despite a C$3.2 billion ($3.1 billion) expansion of its system.

Enbridge, whose lines carry the bulk of Canada's oil exports to the United States, is struggling to cope with booming oil output from the Alberta oil sands and from shale-oil fields such as Bakken in North Dakota.

The company expects to complete a huge expansion of its North American pipeline network in 2014, bulking up its massive mainline, which currently ships close to 2 million barrels of crude per day, and tapping new refining markets in Quebec. The planned mainline expansion will add more than half-a-million barrels a day of new capacity within two years.

Enbridge President Al Monaco said the company and partner Enterprise Products Partners LP could add another 250,000 bpd of capacity on the 150,000 bpd Seaway pipeline, which runs from Cushing, Oklahoma, to the U.S. Gulf Coast by yearend, earlier than its previous target for the first quarter of 2013.