TransCanada Corp's Canada-to-United States Keystone oil pipeline was operating normally on Thursday at rates above 500,000 barrels a day, a company spokesman said.
Earlier, Genscape, which independently monitors pipeline and refinery operations, said it detected decreased flow in the line between Hardisty, Alberta, and Steele City, Nebraska.
It estimated a rate early Thursday of 38,000 barrels a day, down from 576,000 barrels a day previously, and said it observed decreased power consumption at all pumping stations.
TransCanada spokesman Grady Semmens said in an email that the company does not comment on changes in flow rate or outages related to "standard operating issues."
The pipeline, with a capacity of 590,000 barrels a day, is the first phase of TransCanada's overall Keystone system and has been in operation since 2010.
The next phase, between Cushing, Oklahoma, and Gulf Coast refineries, is under construction. The contentious Keystone XL project, between Alberta and southern Nebraska, still requires U.S. federal approval after U.S. President Barack Obama rejected the initial application last year.
TransCanada re-applied to build that $5.3 billion portion and hopes for a U.S. regulatory decision in the coming months.