Plains said it was able to confirm a leak from the Rangeland oil pipeline system last week. The provincial government reported an undetermined amount of oil spilled into the Red Deer River.
Stephen Bart, vice president of crude oil operations, said about 1 mile of containment boom was deployed within 12 hours of the incident.
"The good news is that the pipeline wasn't flowing at the time of the release," Bart said.
This meant the volume of the spill is "relatively" small. The rate of water flow through the Red Deer River meant oil leaked from the pipeline was in an area that responders could contain, he added.
Bart said the response would continue until the cleanup is completed and restoration activity for land and water potentially contaminated by the spill was finished.
Plains added that some images broadcast on national television and other media outlets depicted a 2011 spill from its Rainbow oil pipeline.
Canada's Energy Resources Conservation Board said about 28,000 barrels of oil spilled from the pipeline, making it one of the largest spills since the 1970s.
"The Rainbow pipeline release site is now fully remediated and nearly 100 percent reclaimed with natural revegetation occurring," Plains said in a statement.